We value Open Source and make a point to release all our plugins on GitHub under a BSD License.
Inside RubyMine, open the Plugins setting menu.
Mac: Preferences → Plugins
Win: File → Settings… → Plugins
Search for wakatime.
Click the green Install button.
Re-launch RubyMine.
Enter your API Key, then click Save.
Use RubyMine like you normally do and your coding activity will be displayed on your WakaTime Dashboard.