Art -
opengameart.org user Buch - ui sprites (CC-BY)
lospec.com user Chase Stemel - colorpalette (???)
game-icons.net user lorc - unmasked mask icon (CC-BY-3.0)

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