See how it uses LUA_BIN = "bin/lua"? Apparently SL4A is set up to execute a native application in a separate process. Lua for instance builds from a C project. The agcc/ folder probably has something to do with this (just to throw out vague vacuous suggestions ^^ ).
As far as JRuby goes though, I really like Ruboto IRB, a completely separate project. Or is it? At one point I think I heard that Ruboto IRB kinda branched off of SL4A. Not trying to start rumors, just not equipped with a convenient way to check my facts right now. :-p