Stefan Jones sez,
One of the problems faced by early enthusiasts of Dungeons & Dragons was a severe shortage of the actual game. Tactical Studies Rules wasn't up to the job of supplying sufficient copies of a game that burst out of its traditional audience of miniatures wargamers. I remember photocopied sets of the first printing were ubiquitous at gaming hang-outs.
There was an alternative. Long before I was finally able to get my hands on a "white box" edition of Dungeons & Dragons, I was able to get my own copy low-rent competitor, Tunnels & Trolls.
Ken St. Andre's creation was sillier and far more casual than D&D, but you could use it to create adventures just as satisfying. Its basic design also made more sense than Gygax & Arneson's mutant offspring of miniature's rules: The characters' attributes played a direct role in game mechanics.
T&T never had the success of Dungeons & Dragons, but it was responsible for one major innovation (paragraph-based solitaire adventures) and has been through several editions. (One of the works of game writing I'm most proud of is Dark Temple, an epic solo adventure published back in 1994.)
After several years of being out of print, a new edition of T&T is in the works. To fund the development work, the original artistic and design team has put together a Kickstarter, with plenty of interesting reward levels and swag.