What’s So Cool About Magic Portals? is a tiny little system for going through magic portals no matter where you are!
Buy a print copy, or print out the pages and stick them in a notebook to carry them around with you.
They’ve even got dice printed on the pages so you can literally play anywhere (Google might have a dice roller, but does Google work on the other side of a magic portal? Probably not.)
For PDF copies on their own go here.