3 links
Ladislav Mecir's REBOL Articles
fm.vslib.cz
Several excellent technical articles about functions, context and binding, and the REBOL interpreter. Also dialects and scripts.
Tail recursion in REBOL
ll1.ai.mit.edu
Proper tail recursion is unusually difficult to achieve in REBOL. Joe Marshall describes the problem and solution. From LL1: Lightweight Languages Workshop.