Librera is the first ereader app I used before switching to Lithium. Librera is very versatile but rampant with feature creep and feels a bit clunky to use, especially on my low-powered android tablet.
I'm already using Lithium, also FOSS and from F-Droid...
Anyone know how this one compares?
Lithium, iirc, parses only epubs. Librera Pro parses a large number of formats, like PDF, epub, mobi, azw, djvu, and so on. It also supports auto-cropping of white margins in formats that do not support reflowing of text.
Lithium disappeared from F-droid ages ago? I remember switching to Librera.
Book Reader, also on F-Droid, is a great fork of FBReader.