non-lispy metaprogramming

ITT we talk about doing metaprogramming in different ways that idiomatic lithp style (lisp/scheme-style macros, HOFs and lambdas, eval). what are your favorite unusual ways of writing programs that write programs? do you use metaclasses and AST rewriting in dynamic langs? have you ever written self-modifying asm? do you know rebol and red? metalua? mps? m4 macros? template dead dog? or maybe you're FrozenAnus and use the C preprocessor?