Just Want a .dll?
If you don't care about the source and just want a .dll you can get a compiled release from https://github.com/dotless/dotless/downloads
Simply select for the latest successful build and click on the "Artifacts" section, here you'll find the latest compiler exe and any dll's required.
Whats this all about?
This is a project to port the hugely useful Less libary to the .NET world. It give variables, nested rules and operators to CSS.