aka "Midnight at the Well of Souls Role-Playing System"
From the back of the box:
"Entered by a thousand gateways built by a race lost in the clouds of time[,] the planet its dwellers called the Well World turned beings of every kind into something else ...
"Journey to the Well World or adventure in the domains of the Com Worlds. Either way, this fast-paced science fiction role-playing game will fascinate you and your friends for hours"
Based on the books by Jack L. Chalker