Requirements
Vim
vim-plug is known to work with Vim 7.0 or above, however 8.0 is recommended for parallel installer without dependencies.
Git
Most of the features should work with Git 1.7 or above.
However, installing plugins with tags is known to fail if Git is older than 1.7.10.
Git 1.8 or greater is recommended.
Neovim
Simply install neovim to make use of the job based installer.
Parallel installer
Vim 8 / Neovim
vim-plug starts non-blocking, parallel installer on Vim 8 and Neovim. You can append --sync flag to PlugInstall or PlugUpdate command to make the installer block the control until completion.
Vim 7
If you use Vim 7, Ruby or Python is required to start parallel installer.
Ruby
The ruby installer requires the ruby interpreter (1.8.7+) and vim compiled with +ruby support.
You can check it works inside vim by:
:ruby puts 'ruby works'
Python 2 or 3
The python installer requires python version >= 2.6 or any version of 3.
Python 2.7 is recommended as many plugins still require +python.
Vim must be compiled with +python or +python3.
To check the interfaces work:
+python: :python print 'python 2 works'+python3: :python print('python 3 works')