RePak is a modding tool used to compile various types of game assets into RPak (Respawn Pak) files that can be used in Apex Legends (R5Reloaded) and Titanfall 2 (Northstar).
Important
Full documentation for the tool is currently being written.
Until then, please refer to Northstar's own guide on how to use RePak: https://docs.northstar.tf/Modding/repak/