I've just found a cool little Java app (installers available for Windows, OSX) for validating web sites called the Total Validator Tool. And it's free (though not open-source) so it's even better. Another tool to add to the utility belt.

Anyone who does Ruby on Rails development should familiarize themselves with mod_rails aka Phusion Passenger as the brand new v2 RC is just amazing. Just take a look at those improvements: from buffered uploads so apps don't get stuck, to a tremendous reduction in the memory usage, Rack and WSGI support (yeah, it can run Python apps!), improved startup time...