Yes, I know that less was in first place written for node.js. But I really want to use it without adding node.js to my server, or learning how it works.
Is there some implementations of less written in other languages? Or maybe something similar to less?
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.