Adventurers! strips RPG design down to bare essentials to handle all the necessary mechanics - three stats, a skill list, and descriptive phrases. The system uses just 2d6, modified by a few pips to either side and a simple system of advantage vs disadvantage. The result is a system that focuses on the descriptions of the characters and action rather than tactical complexity. It's similar to other rules-lite systems that emphasize character choices rather than the ability to min-max point scores.
The only real downside is that most opponents can be reduced to a few hit points, a stat bump, and an ability that gives them an advantage. It's up to the GM to differentiate elements through description. Other systems focus on a single element and treat them in more detail, like the tactical game in Savage Worlds or the narrative game in Fate. Adventurers! does only what's needed, but it does it very well indeed. The various settings add specific elements of that setting to the basic rules, and really make the game shine.
Even though the ad copy claims the main game and each setting are only two pages, you always get at least four pages of material - sometimes more. Because all of the settings use the same extremely lite set of rules, switching between them for different cmapaigns or pulling character concepts from multiple genres is easy and convenient. My only complaint is that the downloads come in a ZIP file full of multiple PDF files, which means I can't download them directly to my tablet as a single, readable file. I can cope with that.
[5 of 5 Stars!]