The WakaTime plugin works for Visual Studio for Mac, MonoDevelop, Xamarin Studio and is open-source on GitHub.
Inside MonoDevelop/Xamarin Studio navigate to Tools → Add-in Manager.
(Visual Studio → Extensions… in Visual Studio for Mac)
Click the Gallery tab, then search for wakatime.
Click the Install button and then when add-in installation dialog popups click Install.
On MonoDevelop/Xamarin Studio versions prior to 5.10 you might get an error message, just ignore it.
Enter your API key
, then click Apply.
You might have to restart your IDE.
Use your IDE like you normally do and your coding activity will be displayed on your WakaTime Dashboard.