Pocket Scheme is a R4RS Scheme for Windows CE Handheld PCs and Windows CE or Windows Mobile Pocket PCs.

Its macros are unhygienic define-macro macros. Its numeric tower does not include complex numbers in either polar or rectangular notation. Its lack of syntax-rules macros, multiple values, and arity-2 eval prevent it from claiming full R5RS support.

It can host JACAL, albeit not too gracefully (better on a keyboarded Handheld PC than a frequently-keyboardless Pocket PC).

For PDAs running the Palm OS, you instead want LispMe.