RHEL source code is freely available under the GPL (GNU General Public License) for those who want to compile it themselves, but the actual finished product costs money. Yes, there is CentOS, a free-to-download clone of RHEL compiled from the source code by CentOS developers. But Red Hat charges a premium for RHEL because it's (theoretically) guaranteed to work—Red Hat and third-party software vendors make sure that applications running on RHEL are not broken when the operating system is updated.

Overtone is an open source audio environment being created to explore musical ideas from synthesis and sampling to instrument building, live-coding and collaborative jamming. We use the SuperCollider synth server as the audio engine, with Clojure being used to develop the APIs and the application. Synthesizers, effects, analyzers and musical generators can be programmed in Clojure.

JWChat is a full featured, web-based Jabber™ client. Written using AJAX technology it relies on JavaScript and HTML at the client-side only. It supports basic
jabber instant messaging, roster management and groupchats based on the
MUC protocol.