ArcGIS certainly is one of the most powerful and used within the environment of GIS, therefore there is a variety of companies and individuals who develop extensions, scripts and other tools to increase capacities. For this reason, below is a list of free and paid extensions.
Free ArcGIS extensions.
HEC-GeoRAS, is a GIS extension that provides the user with a set of procedures, tools, and utilities for the preparation of GIS data for import into HEC-RAS and generation of GIS data from RAS output. While the GeoRAS extension is designed for users with limited geographic information systems (GIS) experience, knowledge of GIS is advantageous. Users, however, must have experience modeling with HEC-RAS and have a thorough understanding of river hydraulics to properly create and interpret GIS data sets.
Compatible with ArcGIS: 8.x, 9.x, 10.x
DNR Garmin Application, was built to transfer data between Garmin GPS handheld receivers and various GIS software packages. The application has a real-time tracking mode that allows users to follow their progress on the ground within an ArcView View Document, ArcMap Data Frame, or Landview Map. This real-time track log can be saved as either points or lines as a set of graphics or in a shapefile.
Compatible with ArcGIS: 8.x, 9.x.
River Bathymetry Toolkit (RBT), is a suite of GIS tools that work within the ESRI ArcGIS Desktop software. The RBT allows users to describe and measure river channels using high resolution digital elevation models (DEM). The DEMs can be derived from airborne remote sensing, such as LiDAR, or from ground based topographic surveys.
Compatible with ArcGIS: 9.3, 10.x
TauDEM, is a suite of Digital Elevation Model (DEM) tools for the extraction and analysis of hydrologic information from topography as represented by a DEM. TauDEM provides the following capability: Development of hydrologically correct (pit removed) DEMs using the flooding approach, Calculates flow paths (directions) and slopes, Calculates contributing area using single and multiple flow direction methods, Multiple methods for the delineation of stream networks including topographic form-based methods sensitive to spatially variable drainage density, Objective methods for determination of the channel network delineation threshold based on stream drops, Delineation of watersheds and subwatersheds draining to each stream segment and association between watershed and segment attributes for setting up hydrologic models..
Compatible with ArcGIS: 9.x, 10.
ArcGIS Toolbar, one of the goals of the Internet Access and Data Distribution (IADD) is to create opportunities for our customers to have better access to our data and to increase the functionality of that data. With that goal in mind the ArcGIS Toolbar is an extension or Add-on to be used with the ESRI ArcMap product. The Toolbar functions within the ArcGIS Toolbox and the ArcMap Toolbar. This enhancement creates a series of buttons on the Toolbar within the GIS that allows the user to access Seamless Data Distribution System (SDDS). The purpose of the enhanced tools are to allow the user to define an area of interest (AOI), select products or options for downloading products, and then download the product to a local disk. The capabilities available in ArcMap would allow for more client options: add preview, index and outline layers, template selection, reprojection, and import the downloaded products into the current map overlay. All of this can be done without leaving the ArcMap environment. With the functions included with the ArcGIS toolbox, users may allow for client-side scripting, model-building, and easier integration in local ArcGIS based development.
Compatible with ArcGIS: 9.3, 10.
ArcGIS Editor for OpenStreetMap, is designed to help ArcGIS users to become active members in the growing community of users building an open and freely available database of geographic data. The ArcGIS Editor for OpenStreetMap allows you to use ArcGIS tools for working with OpenStreetMap data. You can install tools for ArcGIS Desktop, or a Feature Service component that leverages ArcGIS Server. The Desktop tools allow you to download data from the OpenStreetMap servers and store it locally in a geodatabase. You can then use the familiar editing environment of ArcGIS Desktop to create, modify, do network analysis, or delete data. Once you are done editing, you can post back the edit changes to OSM to make them available to all OSM users. The Server Component allows you to quickly create ArcGIS Server feature services based on OSM data for consuming and editing in a variety of map viewers.
Compatible with ArcGIS 10.
Hawth’s Analysis Tools for ArcGIS, is an extension for ESRI’s ArcGIS (specifically ArcMap). It is designed to perform spatial analysis and functions that cannot be conveniently accomplished with out-of-the-box ArcGIS. Most of these analysis tools have been written within the context of the ecological applications I am involved in (movement analysis, resource selection, predator prey interactions and trophic cascades). However, they have been created in such a way as to be as broadly applicable as possible such that I hope people from many disciplines will find use in this set of tools.
Compatible with ArcGIS 8.x, 9.x.
Arc Hydro Tools, is an ArcGIS-based system geared to support water resources applications. It consists of two key components: Arc Hydro Data Model and Arc Hydro Tools. These two components, together with the generic programming framework, provide a basic database design and a set of tools that facilitate the analyses often performed in the water resources area. Arc Hydro is intended to provide the initial functionality that can then be expanded by adding to it database structures and functions required by a specific task or application.
Compatible with ArcGIS 8.x, 9.x, 10.1.
Tools for Graphics and Shapes, this extension includes a large suite of tools for calculating geometric attributes of vector features and for selecting and naming graphics. All tools are available at the ArcView license level. Among many other functions, this extension offers tools for calculating the true area and centroid of polygons as they lay on the sphere, thereby avoiding errors caused by projection distortions. This extension also offers tools to calculate true lengths of polylines as they lie on the spheroid, using Vincenty’s equations. This manual thoroughly explains all algorithms used to calculate geometric attributes on the sphere and spheroid.
Compatible with ArcGIS: 9.x, 10.
Jenness Enterprises ArcGIS Tools, a series of powerful free tools for ArcView 3.x, and ArcGIS such as: Corridor Designer Evaluation Tools for the movement of local species, Land Facet Corridor Designer desing wildlife relationships within climate change, Repeating Shapes for systematic division equal of a surface, DEM Surface Tools generates a variety of landscape features to surface usisng digital elevation models, Raster Extractor can extract from ASTER Global Digital Elevation Model.
Payment ArcGIS extensions.
XtoolsPro, is a comprehensive set of useful vector spatial analysis, shape conversion, and table management tools for ArcGIS that greatly enhances ArcGIS functionality and allows ArcGIS users to get to a new level of efficiency and performance. XTools Pro includes more than 70 tools for vector spatial analysis, shape conversion, and table management and more than 40 geoprocessing tools. The most essential functions are collected in a single toolbar for ArcGIS users. New useful tools help save your time and open up unique opportunities for working with geographical data.
Compatible with ArcView 3.x y ArcGIS 8.x, 9.x, 10.x
CrossView, by the time exhausting process of switching software programs to achieve cross section detail for topographic, geologic and hydrologic profile visualizations, the developers of CrossView were compelled to fill this gap between GIS and CAD or Illustrator. A-Prime Software began developing a product that would simply enhance ESRI’s features without creating an entirely new GIS software platform that would take users precious time to learn.
Compatible with ArcGIS 9.x, 10.
Arc Hydro Groundwater, based on the Arc Hydro Groundwater data model, the tools will enable you to take advantage of the ArcGIS platform to archive, manage, and visualize your groundwater information. Expand your ArcGIS software with groundwater and subsurface geoprocessing tools developed in collaboration with ESRI. Georeference subsurface data including boreholes, sketched cross sections, and geovolumes. Reduce the need for multiple applications – visualize model data inside of ArcGIS.
Compatible with ArcGIS 9.x, 10.
Arc2Earth, was designed for ArcGIS Desktop users across industries who are seeking a bridge between ArcGIS and other GIS solutions. Arc2Earth provides a simple and effective platform for: Publishing and maintaining up-to-date online maps for public consumption. Sharing map data to facilitate private collaboration across geographies, departments and/or organizations. Integrating continually updated Google imagery into ArcGIS. Enjoying fast, two-way communication and updates via secure cloud computing.
Compatible with ArcGIS 9.x, 10.
GeoCat, an extension for Esri ArcGIS® Desktop, has been designed to make the process of publishing geospatial data on the internet as easy as hitting the Publish button. From your project in ArcGIS Desktop, you are literally only one click away from publishing your geographic data and metadata on the Internet using an open source server platform.
Compatible with ArcGIS 9.x, 10.
CarryMap, is a unique solution for reproducing your ArcGIS maps as self sufficient distributable electronic map applications for desktop computers, Windows mobile, Apple iOS, and Android devices (CarryMap application for iOS and Android devices is available at App Store and Google Play Market, respectively).
Compatible with ArcGIS 9.x, 10.
TAB Reader, with TAB Reader tools you will be able to import TAB symbology to ArcGIS, batch convert TAB symbology from TAB files to ArcGIS layer (.lyr) files, as well as import MapInfo workspaces (.wor) to ArcGIS ArcMap documents (.mxd).
Compatible with ArcGIS 8.x, 9.x, 10.
Well Tracking, is an ArcGIS based solution for effective management and visualization of 3D spatial well drilling data on a corporate level. WellTracking automates all spatial data management processes related to the life-cycle of the well allowing monitoring and controlling all stages of the drilling process.
Compatible with ArcGIS 9.x.
Add-ins / Arcscripts for ArcGIS
ArcScripts for ESRI, in the ArcGIS Resource Center, we offer a wealth of powerful scripts developed by a valuable community of experts, a site entirely recommended, you can download tools such as: Synchronized Google Earth with View map of ArcMap, Integrating ArcMap with Google Earth, KML 2 SHP Converter for points, lines and polygons, Export to KLM, etc.
In the ArcGIS Resource Center, you also found interesting tools such as: Using R in ArcGIS 10, Spatial Statistics ModelBuilder Tutorial for ArcGIS 10, Convert GPS Files (KML, GPX, WPT, PLT) to Shapefiles, Additional Conversion – Generic Tools, ArcPhoto, Create 2D and 3D geologic cross sections, Compress Imagery, etc.
ET Spatial Techniques, of Ianko Tchoukanski to add functionality and enhance ArcGIS, payment tools as: ET GeoWizards, ET GeoTools y ET Surface. also free tools like: EasyCalculate, EditTools for ArcView 3.x, ProfileExtractor, 3DInControl, Watershed, Datum Converter y ArrangeDocuments.
Please if you find any errors or want to suggest an extension can leave a comment.