Acropora is described as 'Voxelogic develops voxel-based modeling tools for terrains as well as 3D objects' and is an app in the Photos & Graphics category. There are more than 25 alternatives to Acropora for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and Steam. The best alternative is 3D-Coat. It's not free, so if you're looking for a free alternative, you could try MagicaVoxel or Terragen. Other great apps like Acropora are Goxel (Free, Open Source), Vue (Paid), VoxelShop (Free, Open Source) and World Machine (Freemium).
Voxel Builder lets you easily create and edit 3D voxel graphics right in your browser. Simply select a colored block and click to draw. Zoom in and out with the mouse and click and drag to navigate around the 3D canvas.
ShapeShop is a new 3D modeling and design tool with a fun, easy-to-learn interface. Sketch-based shape creation and editing tools make it simple to quickly translate your ideas into a 3D shape, and drag-and-drop decal compositing makes texturing simple.