ChessDB - a Free Chess Database

It's a solid chess database, for sure. Nothing else free comes close. It has a well-written tutorial, a solid feature set (lost a point for not being able to print games). I will never be a fan of multi-window UI (for the principal reason that, on windows, trying to switch to the application between tasks usually results in only one window gaining focus, with the rest staying hidden). But if you like that sort of design, this is well done, and does everything it is supposed to. It's stable, well-featured (if a bit disorganized), and reasonably easy to work with.