TF2 by Squad's rules: go down, call for a Medic in real Squad soldier voices from your own copy, and get revived.
Team Fortress 2, played by Squad's rules, with Squad's real soldiers shouting in it.
When you're killed, you don't drop straight to the respawn screen: you go down where you fell, like in Squad, and your merc calls for a Medic in a real Squad soldier's voice.
Play together: Play hosts a game on cp_dustbowl with bots filling empty slots (up to 12 players). The host's address shows up in Melty; a friend who has the mashup opens the TF2 console and types connect <address>.
Your own games, nothing copied: the first Play reads Squad's voice lines straight from your Squad install (a few seconds). Nothing from Squad or TF2 is in the download. You need both Team Fortress 2 and Squad installed.
Credits: designed by Utku, built with Claude. The setup tool includes ooz (GPLv3, source included), vgmstream's Bink Audio decoder (ISC) and wazero (Apache-2.0).