These are snapshots from the 0.2.8 branch that has been alive for far too long.
Later builds from this branch carry a 0.2.9 version tag, even though a real 0.2.9 release is unlikely to ever happen.
*dedicated*: Dedicated server; everything else is the game client/hybrid server
*.exe: Windows installer
*.dmg: Mac drive image
*.package: Linux Autopackage installer
*.deb: Debian packages; must install armagetronad_common*.deb first.
Armagetron*: Portable Linux Apps for 32 bit systems. Just download, mark as executable and run.
*.src.tar.*: Unix and Mac source tarball.
*.src.zip: Windows source zip. Almost identical to the tarball, but has the Unix build system removed and a couple of files converted to DOS mode.
*.bin.tar.bz2: Binary tarball for use with Zero Install on Linux. Best not to manually download those.
*.win32.zip: Binary zip for use with Zero Install on Windows. Best not to manually download those.