Where do you get such software? You can develop web applications yourself (and or even use open source code from existing sites where permitted i.e. no copyright or patent encumbered code), purchase web applications, and downland then install free (aka open source applications). Sourceforge.net is a good source for applications. Be careful as some applications that say they are open source are really not open source. You have to read the fine print.
Note: This instructable requires some knowledge of the linux command line, basic html, a Lamp (Linux, Apache, Mysql, PHP) based web server and administrative rights to the server via sudo.
Try this instructable also: http://www.instructables.com/id/Linux-screen-play/
After doing this instructable, you might also like: http://www.instructables.com/id/Statusnet-the-Twitter-clone-setup/ and or http://www.instructables.com/id/eyeOS/