LSO

The compiled form of LSL scripts - a mostly stack-based language with a reference-counted heap and a very odd function calling convention in which the caller allocates storage for callee's local variables. All the gory details can be found at http://libsecondlife.org/protocol/index.php/LSO, including some opcodes that are implemented in the interpreter but never outputted by the compiler (such as the handy DUP family of instructions).