The repo that I run hosts Signal, whose developers are needlessly hostile to F-Droid:
We can include Signal in F-Droid - #13 by fd-fan
https://github.com/LibreSignal/LibreSignal/issues/37
How to get Signal APKs outside of the Google Play Store - #20 by moxie0 - Android Feature Requests - Signal Community
And uGet, which has not submitted itself to F-Droid. (I also believe it has non-Free components in its default build, but a libre build is possible if I’m reading the gradle files correctly.)