We value Open Source and make a point to release all our plugins on GitHub under a BSD License.
Download the .nbm plugin from GitHub releases
Inside Netbeans select Tools → Plugins → Downloaded → Add Plugins…
Select the downloaded nbm file.
Check WakaTime and click the Install button.
Follow the wizard instructions to complete the installation.
Enter your API Key, then click OK.
Use NetBeans like normal and your stats will automatically show on your WakaTime Dashboard.