So many amazing things could be done. The ideal situation is one in which users can quickly and efficiently mark all tools they use and also get them to update that list every ~6 months. It would integrate nicely with Stack Exchange network I think.

http://osx.iusethis.com/ is somewhat like this. you can see the most popular tools in different categories. they dont have a timeline view.

appfresh also has integration with this, where you can check the tools you need and also update them.