This is a single file VM written in C. Lexing/parsing isn't implemented, but it takes instructions and eval()'s them in a big switch statement until it gets a HLT. Currently the program is compiled into the interpreter, but passing it via arguments would be trivial given a lexer that spits out the proper instruction/data values.
Instruction set is currently:
PSH, // 1 arg, value
POP, // 1 arg, register
SET, // 2 arg, value, register
MOV, // 2 arg, register, register
ADD, // 0 arg
DSP, // 1 arg, register
CMP, // 2 args, register, register
JEQ, // 1 arg, int # instructions to jump
INP, // 1 arg, register
HLT, // 0 arg
which are all in an enum. Example program is in the program constant