Obtaining RTAIhttp://www.rtai.org => section Download (http://www.aero.polimi.it/RTAI/)
or
https://gna.org/projects/rtai => section Files (http://download.gna.org/rtai/)
If you want to download the latest vesion of RTAI, use CVS :
Browse cvs here : http://cvs.gna.org/viewcvs/rtai/
Instruction for anonymous acces here https://gna.org/cvs/?group=rtai
Other RTAI web site (new one ?) : http://www.fdn.fr/~brouchou/rtai/
You should probably also get the rtai examples called "showroom": http://download.gna.org/rtai/nightly/