Overlord is an extension. This means it's installation is a typically a bit trickier than installing a script like RubberHose.
To reduce the complexity of installing extensions, the smart folks at aescripts.com built a really awesome Extension Installer that will make your life a lot easier to get up and running with Overlord. So download and install it.
- Unzip Overlord
- Drag Overlord.zxp into ZXP Installer
- Close and reopen After Effects
- Open the Window menu, find the Extension group and you should see Overlord