Into the Demon Idol is a system neutral mini-adventure by Jobe Bittman. It was originally created for a one page dungeon contest. The original one page version can be found here. This low level (0-3) adventure is 18 pages. The basical plot is that lizard folk tribes are uniting and it looks grim for goodly folk, that is until local village elders inform brave adventurers that there may be magic relics of bygone eras in the local ruins that can help. The item in question just happens to be the demon idol from David Trampier's classic cover, which is in reality a magical mech of destruction! In the course of the adventure the party (hopefully) gets to the idol, figures out how to use it, and disrupts the gathering that will unify the blood thirsty lizard man tribes.
Despite being system neutral, this is designed with some form of D&D in mind. It make use of skill checks (but doesn't give set target numbers) and some game terminology, but it does so in most basic turns. If, for example, there is a ring of fire resistance mentioned, the stats are given. You assume it has the standard stats for one of those for your rules set. There are some new monsters and they are given stats, but the stats aren't a part of the adventure booklet. The stat blocks are on a double sided book mark and the monsters have stats for Labyrinth Lord, Dungeon Crawl Classics, and Swords & Wizardry (though could be easily adapted to any version of D&D).
This adventure seems like a lot of fun. It's over the top, but not quite to gonzo levels. There are also some nice nods, such as "Wampler's General Store," which I assume is shout out to Goodman Games Jim Wampler. I'm picturing a fun old school sandbox in mind using this and material from some other adventures (Keep on the Borderlands, The Horrendous Heap of 16 Cities, Death Frost Doom, and A Single, Small Cut).
You can purchase the digest-sized mini-adventure here.