Online Minecraft Alternatives
Minecraft is not available as a web app but there are plenty of alternatives that runs in the browser with similar functionality. The most popular Online alternative is 
ClassiCube, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to Minecraft and 11 are available as a web app so hopefully you can find a suitable replacement. Other interesting Online alternatives to Minecraft are 
Block Story (Freemium), 
iLands (Free), 
Mine Blocks (Free) and 
Adventure Box (Paid).
- An alternative to the Java web game "Minecraft Classic" that was listed on the official Minecraft site but taken down in 2016-2017. View 7 alternatives to ClassiCube
- Free • Open Source
- Mac
- Windows
- Linux
- Online
ClassiCube vs Minecraft
It has fun servers, and I found it when I was searching for a similar game for Chromebook.Free "Creative Mode" (though outdated). - Block Story combines a mineable blocky world pioneered by Infiniminer and made popular by Minecraft with exciting and addictive role playing. View 47 alternatives to Block Story
- Build your dream island in a 3D, blocky world! Play with friends in real-time! - Claim your own randomly-generated iLand and customize it to your liking. View 51 alternatives to iLands
- A free 2D Minecraft browser game, made in Flash!. View 57 alternatives to Mine Blocks
- Adventure Box lets anyone import Minecraft maps, create and share their web voxel games and worlds. View 13 alternatives to Adventure Box
- Minecraft Buzz is a Minecraft Server List dedicated to helping players find amazing servers for Minecraft of all game modes and versions. View 2 alternatives to Minecraft Buzz
- To allow people playing Minecraft to connect online & view a range of servers to join, for free. Server owners can post the details allowing them to attract more players, quickly & easily. Represent entire series of Minecraft Server Lists games. View 87 alternatives to Minecraft Server Lists
- Multiplayer Voxel Survival in C99, includes a badly written implementation of LISP. View 9 alternatives to WolkenWelten
- Paper Minecraft is a building game for you to experience everything from quarrying stone and wood to making tools to building buildings. Before starting the game, you can choose a character and a play mode (survival, creative or peace game mode). View 11 alternatives to Paper Minecraft
- This is a MineCraft based online multiplayer mining game. Mine, craft and build with you're friends! View 23 alternatives to Block Miner
Discontinued
The games servers were shut down in June 2016. http://www.kongregate.com/forums/125-block-miner/topics/647377-announcement-block-miner-is-shut-down
- Freemium • Proprietary
- Online