With a minimal change, SciTE's Python lexer can be used for formatting of Ren'Py scripts. The property settings below can be used to configure SciTE 2.x to better deal with Ren'Py. Note, however, that properties in SciTE are global, and not per-buffer; if you're switching between Python and Ren'Py files, you'll need to write some Lua code to handle swapping property values whenever tabs are changed and files opened.