open social source

Currently doing a report on social media and seeing a lot of convergence with open source systems.
which has got me wondering what is the main application for an open source system with in an local authority

is it for example a cms for intranet or possible a websites or would it be more things like paint.net to replace photo shop or paint shop installs or perhaps moving to google docs or even open office to replace Microsoft’s cash drain ?

http://www.opensourcecms.com/ - site grouping together all the open-source cms system with a tryout system so you can see which one suite you best

http://paint.net/ - powerful photoshop alternative

http://www.openoffice.org/ - as good as office 2003 not sure but dose have some nice touches the potential is there