Searching
I feel like SearXNG goes way under-mentioned. It's a meta search engine, basically a search engine aggregator...
mobile Apps
Obtainium should be mentioned more. It's not technically European, as its creator is Canadian, but it's fully open-source. It's an app that helps you manage other open-source apps. I feel like it's a good way to avoid the Google Play Store, if you're looking to use European open-source software.
Passwordmanagers
KeePass is oft mentioned, but KeePassXC is better, IMO. Keepass2Android is the Android equivalent.