By the way, sadly, we didn't have enough time to finish to create and put signposts explaining controls. So here's how you play:
You need to target the signposts and hook them (by holding left click) with the magnetic grappling hook to brake your minecart and avoid losing the gold in it. But if you keep a signpost hook for too long, the rope will break, so you need to release the right click soon enough ^^
(The escape key let you restart, and yeah you can't close the game without alt-F4, but why would you close it ? :p )