Check out: http://nodexl.codeplex.com/

Other open tools include: Twitris: http://twitris.knoesis.org but you can only analyze some of the events we decide to follow (eg Hurricane Sandy, Occupy Wall Street, Oklahoma Tornado) as we d on have computing power to track many events simultaneously.

Companies like Topsy, Raidant 6,.... have proprietary tools.

Check the Partner tool

http://www.partnertool.net/

There is a nice compilation of SNA tools here: http://en.wikipedia.org/wiki/Social_network_analysis_software

Just search for "browser" - to get the online tools ( I think there are 4 mentioned in the list)

Check this: https://kumu.io/