When I heard Phigros was completely free, my first cynical reaction was that it must be free with in-app purchases, or free with ads, or free while mining bitcoin, etc. But no, it is a completely free rhythm game featuring a bunch of indie EDM artists. (I've seen some players purchase the devs' other paid game purely to support their work on this one.) The charts are done with incredible attention to detail: easy charts are more straightforwardly "gimmicky", while the harder difficulties include interesting patterns and techniques. On top of that, there are plenty of hidden songs and annual April Fools jokes that elicit the same joy as an ARG. It's a brilliant little game with a lot of love put into it--and as it's free, there's really no downside to checking it out.

The only drawbacks are (1) if you're trying to follow the alleged "plot," a lot of the unlockable documents are not translated (makes sense, that's a huge time sink for a free game), (2) it takes ages to unlock all the singles, (3) no cloud save unless you have a Bilibili account (or use outside-of-the-box methods).