For a piece of FLOSS (free/libre and open source software) to be here, it has to both be personally useful and I have to like it a-lot:
environment: Debian, zellij, fish
web browser: Firefox (laptop and mobile)
text editor: Helix
development: Helix, Rust toolchain (cargo, rustfmt, rustdoc, rust-analyzer)
chat: Zulip
search: ripgrep
audio/video: AntennaPod, VLC, Transmission
monitoring: top (part of procps suite)
documentation: mdBook