Art -
opengameart.org user Buch - ui sprites (CC-BY)
opengameart.org user Yughues - textures (CC0)
opengameart.org user Admurin - ui sprites (GPL3)
opengameart.org user JStatz - textures (CC0)

Software -
Matthias Richter (github.com user vrld) - hc.lua (MIT)
Michelle Bu, Eric Zhang, and contributing authors - PeerJS (MIT)