What app do you use to read ebooks?

I'm looking for recommendations. I usually use Overdrive with books I've downloaded (I think in the epub format). But now I hear that Overdrive is no longer being supported (I think the company wants people to use their Libby app instead). I'm hoping to find something open source and privacy minded. Also not wild about what Overdrive is doing to public libraries.

Crossposted on the kbin books magazine.