GeomLab is a system developed by Mike Spivey of Oxford University, to enable complex recursive patterns (of the type immortalised by Escher) to be created easily even by novice programmers. Spivey's GeomLab system (which requires Java to be installed on your machine, and gives appropriate instructions) is available from GeomLab at Oxford University.

Peter Henderson's paper on Functional Geometry, the theory behind GeomLab, is available from: Peter Henderson, "Functional Geometry", in Higher Order and Symbolic Computation, Vol 15, pp. 349-365, 2002.

An interesting (but technically demanding) book on the ways in which functional programming can be used to provide powerful but accessible programming systems for entertainment and education is The Fun of Programming.