Awesome
Quail 
Unofficial but officially accepted esa app 🐦
Install
macOS 10.10 (Yosemite)+, Windows and Linux are supported.
macOS
Download and extract .zip, and move Quail.app to /Applications.
Alternatively, if you use Homebrew, you can install via:
$ brew install --cask quail
Windows
Download and extract .zip, and move Quail.exe to some location.
Linux
Download and extract .zip, and move Quail to some location.