Download
There are several ways to get the game. Choose your favorite.
Direct download:
It does not get simpler than this. Choose the file you want, download it, install it, play it.
Itch
If you prefer it then you can also fint the game on itch.io. This works with the Itch.io App too so you can enjoy auto updating.
Linux packages
Debian and Ubuntu users might choose to install the blockattack package instead: sudo apt-get install blockattack
The versions are not always up to date but they recent enough for most players. Check versions on pkgs.org
Older versions
Old versions can be found on the GitHub release section or Source forge download section
The Puzzle Level Editor:
It you want to create custom puzzles for the puzzle mode then you’ll want the puzzle level editor. Otherwise you do not need it.
Puzzle Level Editor v2 in Java (All OSs)
Download info
Number of download from GitHub (from 2.0.0): 
Number of downloads from SourceForge (up to 1.4.2): 
Development version
The source is now hosted in a git repository at GitHub here.
The master branch contains the development version for 2.X.Y and is considerable different from 1.4.2.
1.4.2 can be found in its own branch.