1. Wallabag, yes i selfhost it and use it every day!
2. Gelli, didn't realise that, i guess it does everything it has to do for me, no complaints or bugs that i know of :)
3. Ntfy, i use it exclusively for my selfhosted apps, but i can imagine broader usage. But still i would file it under selfhosting ;)
4. Linkdy, hmm, you're making me second guess the app
5. LT, shame, it's really good. But I understand

Ok, here's my contribution

Selfhosted

Wallabag - Save and classify articles, read them later, freely

https://f-droid.org/en/packages/fr.gaulupeau.apps.InThePoche/

Gelli - Native music player for Jellyfin

https://f-droid.org/en/packages/com.dkanada.gramophone/

Ntfy - Send notifications to your phone from any script using PUT/POST requests

https://f-droid.org/en/packages/io.heckel.ntfy/

Clipious - Client for Invidious, the privacy focused YouTube front end.

https://f-droid.org/en/packages/com.github.lamarios.clipious/

Linkdy - Linkdy is a Linkding client sorry, google play, no ads, has github page

https://play.google.com/store/apps/details?id=com.jgeek00.linkdy

https://github.com/JGeek00/linkdy

Language learning

Language transfer - great language resource, sorry google play, but no ads, has github page

https://play.google.com/store/apps/details?id=org.languagetransfer&hl=en_US&gl=US

https://github.com/language-transfer/lt-app

edit: linebreaks

Nice! Thanks a lot, found some I hadn't heard of before