Spook started out as a light weight replacement for guard but has become more than that over time. It is mostly written in MoonScript, a language that compiles to Lua - with a sprinkle of C. It's built as a single binary. The ridiculously fast LuaJIT VM is embedded and compiled with Lua 5.2 compatibility. Extensions are easily written in MoonScript, which is also part of the compiled binary. While spook may seem to be geared towards running tests in a feedback loop, there are many other potential uses. For some inspiration, check out my i3bar implementation moonbar for the i3 window manager which is also using a Spookfile but is doing something very different. Otherwise the Spookfile in this repo and the examples in the readme should point you in the right direction if you're just looking for a lightweight test feedback loop runner.