Undobranche_viewer.vim is a project mainly written in Vim Script, it's free.
Undo Branches Explorer
This is a mirror of http://www.vim.org/scripts/script.php?script_id=2141
Vim7 Undo Branches Explorer. See ':help undo-branches', also.
Copy the undobranch_viewer.vim script to the $HOME/.vim/plugin or the $HOME/vimfiles/plugin. Refer to the ':help add-plugin', ':help add-global-plugin' and ':help runtimepath' topics for more details about Vim plugins.
Restart Vim.
This script requires tlib (vimscript #1863) to be installed.