less css server-side, but without node.js?

You could take a look at SCSS. The compilation of files into CSS is done by a Ruby script which is very easy to get set up (even on Windows), and the syntax and feature list is almost identical. I'd even say that the documentation of SCSS is better than LESS.

That said, I have managed to get LESS compilation running locally by running the file in a Javascript engine (in my case, Komodo Edit's macro system is powered by Javascript, but it could work with Rhino or V8). You do have to modify the source a little, to simulate the window object. I got a lot of help by looking at the code of the Less Engine project, which basically allows Less to be executed within a JVM.

There is a Windows LESS compiler for .NET and a standalone version of it as well. I find this latter considerably better (i.e. fewer bugs) than less.js, although both are pretty odd in the way they handle comments: less.js doesn't understand two comments in a row, and lessc.exe doesn't understand comments inside selectors. I really don't see the point of compiling the .less file at the client once per page download per client when you could have done it once for the universe at build time.

There is also a Python implementation of SCSS: http://packages.python.org/scss/. It works quite well and includes a watch folder function.