Gems of the Deep is a simple side-scrolling platformer game initially created in 48-hours during the Ludum Dare #29 competition. It features dynamically-generated and destructable worlds, where the objective is for the player to jetpack through caverns and collect all the gems while avoiding baddies like spiders and bats.
You can see the original competition entry page here.
After the competition, the game was developed further, into the screenshots you see above, with improved graphics and gameplay.
This game was created in Java, so you will need to have that installed in order to play it (at least version 7), even if you download the Windows .exe version. The .exe is simply to make it easier to launch for Windows users.