On my laptop:

• Void Linux
• GNOME (desktop environment)
• gThumb (image viewer that can do simple edits)
• Firefox (the famous web browser)
  • uBlock Origin (content blocker that blocks ads, trackers, etc. out of the box)
  • SponsorBlock (automatically skips sponsor segments in YouTube videos)
• Betterbird (fork of the Thunderbird email client, with various QoL tweaks)
• GIMP (image editor)
• Kdenlive (video editor)
• virt-manager (manage QEMU virtual machines)
• Celluloid (media player)
• yt-dlp (command-line utility for downloading YouTube videos, and the basis of some graphical apps as well)
• Bottles (if you want to use Wine to run Windows apps, without too many headaches)
• Foliate (.epub ebook reader)
• OBS (for screen recording and livestreaming)
• Code - OSS (code editor, “clean” version of Visual Studio Code without “Microsoft-specific customizations”)
• Tenacity (fork of the Audacity audio editor without opt-out telemetry)

On my Android phone:

• F-Droid (app store with FOSS apps only)
• Obtainium (auto-updater for apps hosted on GitHub, GitLab, etc.)
• Heliboard (simple keyboard app)
• Material Files (file manager)
• Metro (local music library player)
• Iceraven (Firefox fork with a few tweaks)
• Voyager (mobile client for Lemmy, similar to the obsolete Reddit clients Apollo and Slide)
• Fedilab (client for Mastodon and similar Fediverse services)
• Termux (run Linux CLI applications on Android)
• Thunderbird for Android (simple email client for Android and the successor to K-9 Mail)
• MJ PDF Reader
• Binary Eye (simple QR code scanner)

Cross-platform:

• LocalSend (simple file transfer between devices on the same network)
• Bitwarden client apps (to manage passwords. I use the Vaultwarden instance @ tchncs.de)
• Mullvad VPN client

If we can count FOSS modifications of proprietary apps:

• YouTube Revanced (the official YouTube app, but you don’t get ads, you can play videos in the background, you get SponsorBlock, etc.) (follow this guide for auto-updates)
• Vesktop (desktop client for Discord, has Vencord preinstalled and supports Linux screen sharing)
• Prism Launcher (Minecraft: Java Edition launcher that allows you to easily manage different “instances” of the game. Good for playing with different mods and/or versions)
• Fabulously Optimized (modpack for Minecraft: Java Edition, that improves performance and adds some minor QoL features)

addendum: I’d like to use Matrix (via the Element client) and Signal more, but most of the people I know are on Discord and WhatsApp instead.