There is only 1 game that I know of right now (changes subject to follow in further replies on this thread) where open gaming is allowed for people to just drop-in and start playing.
Normally every week, friends and I play D&D at Gator's Video in downtown Leavenworth (at 720 Shawnee) every Sunday at 1 pm. The game is HISTORICAL-Earth D&D via the 3.5 edition ruleset, with a small set of house rules. We are currently at level-14.
Because of the Easter holiday today, our gameplay resumes next weekend. Anyone interested should just show up around 12:30 or so, so that 1 of us can get you started (subject to DM approval, being that I am not the DM).
2 other friends of mine (including myself) have imminent plans to start other, new game campaigns soon, most likely AD&D 2nd edition in Forgotten Realms, AND my own imminent campaign with Dragonlance War of the Lance with 3.5, at our home locations instead of at Gator's Video (stay tuned to this thread for updates / further news on this).
NOTE: there is also a Pathfinder Dragonlance Age of Mortals campaign that i am playing in, on Wednesday nights at 6pm, but the DM is NOT allowing new players at this time. But come watch anyway and get to know us, some! You never know what could develop in the future and it would be good to meet other new players around!