You are a lone outsider in a strange, non-Euclidean world.. As a Rogue, your goal is to collect as many treasures as possible. However, collecting treasures attracts dangerous monsters (on the other hand, killing the monsters allows more treasures to be generated).
Collecting enough treasure also allows you to find rare magical orbs, which grant you one-time or time-limited special abilities.
The world is a combination of eleven types of lands. Each land type has specific style (monsters, treasure, magical orbs, terrain features). Collecting treasures only attracts more monsters in lands of the same type, so you can try to collect lots of treasure in several different lands! Ultimately, you will be able to access Hell, and look for the fabulous Orbs of Yendor which are hidden there.
The game is inspired by the roguelike genre (you are not allowed to save as the game is short enough and reloading the same saved file several times would be cheating), as well as puzzle games such as DROD (Deadly Rooms of Death). HyperRogue is one of just few games played on a hyperbolic plane.
Play HyperRogue for free, or download HyperRogue Gold for Euclidean mode, cheats, and online achievements and leaderboards (via Google Games Services). HyperRogue Gold is also updated more frequently (currently, it contains seven more lands with unique mechanics). If you want a small app, download HyperRogue Lite without music. Also play the desktop version of HyperRogue!
More about HyperRogue: http://roguetemple.com/z/hyper.php
5.5a: A major update. Two new lands with new, interesting mechanics. Translations. More features in HyperRogue Gold (online leaderboards and Euclidean mode). Numerous other improvements.
All changes on my blog: http://zenorogue.blogspot.com/search/label/hyper