Out of all the upcoming indie games that I know of, Mythruna is the one I am most excited about. It combines two amazing genres, RPG and Voxel Crafting, into one game. And, it does it with a lot of skill.
Mythruna is decribed on its website as "a game under development attempting to combine serious role playing elements with an endless, living, and completely modifiable randomly generated sandbox world. When completed, Mythruna will be a unique gaming experience."
Developed by developer Paul Speed (pspeed), who has recently taken on a position as an official developer of the engine Mythruna uses, jMonkeyEngine, started work on the game after becoming enamoured with Minecraft, much like the rest of us.
Mythruna was 'born' on Sunday January 30th, 2011 when its first batch of code was checked in, and since then has been very actively developed (Mythruna's Twitter account being updated only 10 hours prior to writing this article).
The gameplay is sparse at the moment. It's essentially Minecraft Creative mode without flight. All of the basic blocks are there (cobblestone, grass, glass, etc.) including a couple of new ones such as White Marble and Black Marble.
Graphically, Mythruna is very impressive, especially for being such an early, Alpha release. The game uses shaders when underwater and up against bumpy surfaces. It all looks very pretty and reminds one quite a bit of a Minecraft-Oblivion mashup.
If you're loving the gameplay found in Minecraft and are looking to try out some similar games, give these games a try. Some are even free to play!
Not all of these are Minecraft clones, however. Infiniminer was actually a huge inspiration to Notch when he started building Minecraft. Also, Notch was part of the team that worked on Wurm Online before leaving to go do his own gig.