Trisquel is based on Ubuntu like other operating systems (Linux Mint, Pop!_OS, Zorin OS, etc.) but they do something unique - they rebuild the Ubuntu packages from source, instead of just including the Ubuntu repos in their software sources.

Trisquel is quite a usable distro for laptops that are 3-4 years old if you have an appropriate wireless card - Atheros 9xxx series cards tend to work well as the ath9k driver is FOSS. That's really the only blocker most people encounter. Why run this over Debian Stable (without adding "non-free" sources) I couldn't tell you. Debian tends to be more up to date than Trisquel since it's usually based on the previous Ubuntu LTS.