Interesting idea. Final Fantasy 12 is my favorite game that allows you to "script" your characters' moves, but you're only ever fighting against the computer. Incorporating this into a programmable MMO seems like it could be very fun, and somewhat parallel to the way stock markets work with everyone using algorithms to compete against each other.
It's not open source. The Firefox Addon captured a visual snapshot and the entire page contents of every non-https page you visited, and stored it to an online database. The website allowed you to search your history, and results were based on number of visits to a page, length of time spent on page, number of times that page was selected as a search result, whether the page was actually bookmarked, etc. It was a very useful tool, but unfortunately the database grew large very fast. I tried to implement a subscription feature to offset server costs, but I had zero subscribers.
The code is all C#/MSSQL/JavaScript/XUL. If anyone's still interested gmail me at my username, and sorry for the off-topic posts!
I created a Firefox Addon and website for it last year that did everything you just wrote about, but I've since closed the project down. Let me know if you or anyone is interested in resurrecting it.
Frequent outages and "write to datastore" errors made me sad. (This was in 2009, don't know whether these issues have been fixed, but I won't be going back.)
I just added Facebook's "Like button" to one of my sites, it was surprisingly easy to do. You can see it in action here: http://www.peoplemarks.com/BruceLee