Also see http://www.ledger-cli.org/

I like how Ledger is essentially just a system for doing arbitrary calculations on "buckets of quantities of stuff" a.k.a. accounts with various currencies and assets. I'm not going to say it's a walk in the park, but I've been able to get it set up so it spits out everything I need to do my Belgian taxes, and before that, everything I needed to do my UK taxes. It doesn't assume anything.

Of course, happy to see some competition in this space. Can only benefit users like me.