Have you tried SciTE? It is a reference/demonstration implementation of a free (and open source) multi-platform text/sourcecode edit component called Scintilla. It uses GTK (but afaik there is also a QT port), so it runs on Linux and Windows (installer) and also may run on *BSD and OS X.

It supports unicode, code folding, syntax highlighting for many languages, multiple buffers (implemented via tabs), sessions (sadly no full project management, but there seems to be an extension for windows), code completion, call tips, has support for building/make process and is highly configurable. But it has no integrated support for snippets and version control.

There is a LUA extension which makes it scriptable.

I really like SciTE and use it lot! :-)