The last ``official'' release was RCCL 5.0, available in compressed tar format. The RCCL User Guide is also available separately as compressed PostScript.
I have a newer version, RCCL 5.1, which I use internally at UBC and which works in real-time under Intel Solaris and also (in simulation only) under Linux. Note that this is just a tarball snapshot of a working system; the docs are somewhat dated and there is lots of ``scratch'' software kicking around.