This is mostly a bugfix release. See CHANGELOG for details.
millfork-0.3.30-win-x64.zip is a 64-bit native Windows build. It runs much faster, but might have extra bugs that don't exist in the jar version.
millfork-0.3.30-linux-x64.tar.gz is a 64-bit native Linux build. This is the second native Linux build, it might have extra bugs not present in the Windows or jar versions.
millfork-0.3.30.zip is your standard cross-platform executable jar release. It requires Java 8 or later to run.