Note: those binaries might become outdated over time. I recommend users taking advantage of nix to install and update unison.
Unison 2.51.2 binaries compiled using ocaml 4.08.1 on Amazon Linux 2012.03.
The unison and ocaml versions are selected to matches ones provided by Formula of Homebrew.
Download this provided binary file and drop into your $PATH. Or simply run
make install