ScummVM is an open source implementation of the SCUMM engine which allows you to run mainly old LucasArts adventure games in systems other than the ones that they were originally designed for. This is done by replacing the old executable files which will no longer run in newer operating systems while still keeping the old data files(in a sense it emulates).
While the engine is open source and thus ported in many operating systems and platforms what you will find here is the Windows version. For more ports feel free to visit the official site.