If for some reason you don't already own Psychonauts on PC, today and tomorrow are your lucky days. Humble Bundle has decided to give away free Steam and DRM-free keys of the game, but you only have today and tomorrow to claim a code.
All you need to do is head over here and make sure you have a Humble account, log into it, and add Psychonauts to your cart as if you were making a purchase. Run through the transaction screen, and the code will be sent to your email box almost instantly. It's worth noting that simply getting the code is not enough to ensure you keep the game. Humble has specified that you need to redeem the code they give you between now and 10 AM Pacific on Saturday, September 30th, 2017, or they will expire.
Granted, that's plenty of time, so there's no excuse not to redeem it.
The Psychonauts giveaway ends at 10 AM PT / 1 PM ET / 6 PM BST on Saturday, September 16th, so you don't have much time on that front.
Psychonauts is considered to be a classic, initially releasing back in 2005 on PS2, the OG Xbox, and PC. It's long awaited sequel was Kickstarted back in January of 2016 and more recently signed a publishing deal with PAYDAY developer, Starbreeze. The game is scheduled to release some time in 2018, but no release date has been made official.