Just mentioning the tools I had not seen on other posts:

Selfhosting

• https://github.com/wallabag/wallabag - Instapaper/Pocket alternative. Has mobile clients and hosted version as well
• https://github.com/paperless-ngx/paperless-ngx - Great document management system, has multiple apps by third party developers
• https://grocy.info/ - ERP for your household (food inventory, grocery list, chores) - there are multiple open source clients for it as well

Android

• https://f-droid.org/en/packages/net.osmand.plus/ - Routing based on OpenStreetmaps
• https://f-droid.org/en/packages/org.oxycblt.auxio/ - Audio player
• https://f-droid.org/en/packages/ws.xsoh.etar/ - Calendar
• https://ntfy.sh/ - Pushbullet alternative, can be selfhosted as well. Works as a - https://unifiedpush.org/users/apps/ provider.