Socilyzer!

Gephi is an open-source software for visualizing and analyzing large networks graphs. Gephi uses a 3D render engine to display graphs in real-time and speed up the exploration. Use Gephi to explore, analyse, spatialise, filter, cluterize, manipulate and export all types of graphs.

Cytoscape is an open source software platform for visualizing complex networks and integrating these with any type of attribute data. A lot of plugins are available for various kinds of problem domains, including bioinformatics, social network analysis, and semantic web.

KeyLines is a JavaScript toolkit used by developers to build powerful network visualization applications, quickly.

NodeXL is a free, open-source template for Microsoft® Excel® 2007 and 2010 that makes it easy to explore network graphs. With NodeXL, you can enter a network edge list in a worksheet, click a button and see your graph, all in the familiar environment of the Excel window.

TouchGraph is the producer of data visualization software TouchGraph Navigator 2. With TouchGraph Navigator 2, users can upload data and create "interactive network visualizations."[1] Users can purchase licenses for either a TouchGraph Navigator Desktop version or TouchGraph Navigator Web, where the user hosts visualizations on their server and views the visualization on a web browser.[1]

Polinode is a tool for collecting information on relationships between people. For example, who works with whom? Who do people go to for advice? And any other question you like. With a powerful survey tool to collect the data and integrated visualization and analysis functionality to explore the network data, Polinode aims to help organizations and non-profits cut through complexity.

UCINET for Windows is a software package for the analysis of social network data.