Interplanetary had Steam trading card support added on 19 June 2014. There are 8 cards in the series, and you'll receive 4 cards at random for purchasing and playing the game.
Champion Humain Railgun Slug
Esteemed Railgun Maintenance Crew Member
Decorated Railgun Gunner
Venerable Chief Railgun Shotmaster
Revered Master General of Planetary Railgun Operations
Council of Interplanetary Defense