Kepler is a web framework built using Lua. Sputnik runs on top of Kepler, but you don't need to know anything about it, since Sputnik users Kepler as an "embedded" framework. Sputnik's installer (see Installation) builds its own install of Kepler and puts all Kepler and Sputnik files in one place. If you end up installing other Kepler applications, they can use their own versions of Kepler. (If this seems wasteful, consider that Kepler+Sputnik jointly take under 1MB.)

Spunik uses Kepler 1.1, which have not been officially released yet but has been quite stable on Unix since early 2007. Sputnik is expected to run on Windows whenever Kepler for Windows becomes available.