I've been spending my free time over the last few weeks on Hand of Fate 2, a deckbuilder with rhythm-based hack'n'slash combat. It's been called a roguelite, and I can understand why, but if it is, it's by far the litest of roguelites. The individual elements aren't especially deep, but they add up to something special. The only thing like it is Hand of Fate 1 on which it improves substantially. Also it runs natively on Linux and doesn't require Steam.