#scifi nerds, I need your help identifying an #SF novel I read decades ago

#scifi nerds, I need your help identifying an #SF novel I read decades ago.
The main characters each possess some sort of device which gives them essentially infinite power. They use it to create and destroy whatever they want, to travel all over the planet, basically anything.
They don't understand how the devices work. Turns out they're connected to giant machines—maybe originally for terraforming?—that are starting to break down, and the knowledge of how to fix them has long since been lost.