Sitecore a .NET content management system I have spoken about on several occasions, have released a light weight version of their content management system called Sitecore Xpress. Sitecore Xpress is free for use on your personal site and is targeted towards developers. Signing up for Sitecore Xpress will give you access to Sitecores Developer Network which enables you to download the latest Sitecore modules and interact with other developers on chat forums for advice, tips and the sharing of code.
Sitecores approach on releasing a "free" version of their software should help to spread its popularity among developers helping them to experiment with the software and create new functionality for it. Similar to the approach used by open source content management systems such as Joomla.