It is nice to see another open source satellite [1]. Usually i only saw used in the satellites, releasing also the hardware part is super cool. However there are also other notable repositories. There is for instance a "space kit" for arduinos [2]. Another interesting project was QB50 [3], many student satellites, from multiple universities worked together to study the lower thermosphere. If you search for QB50, there are multiple public repositories with the code they used.

[1] - https://github.com/Quetzal-1-CubeSat-Team [2] - https://github.com/ArduSat/ArdusatSDK [3] - https://spaceflight101.com/spacecraft/qb50/