Jellyfin★★★★★Great for playing music across my local network, doesn't phone home to a cloud or try to upsell subscriptions.
KeePass Password Managers★★★★★KeePassXC, its browser extension, and KeePass2Android are a nice, clean set of apps to manage your passwords on your OWN desktop and mobile devices, auto-fill websites and apps, and sync over your own server or cloud provider.
Manyverse★★★★☆Takes the pain out of setting up and running SSB. Unfortunately it doesn't overcome SSB's inherent challenges of discovery, data size or multiple devices. (So far?)
Thunderbird (Email and Calendar)★★★★★Stable, capable desktop email application, works well with multiple accounts including Gmail, Nextcloud, easy to set up and use but with advanced settings when you need them. FLOSS.
Windows 10 Mail and Calendar★★★☆☆Not a bad email client. Snappy, works with multiple accounts. Some issues with Nextcloud calendar and contacts. Of course it's being discontinued.
Wine and Crossover★★★★☆THE major compatibility tool for Windows apps on Linux or macOS, including SteamOS. And a commercial distribution with installers and support.