Heavdrones are HTech devices used for monitoring and control of various systems. They communicate with various control backends using SPUDNET. In all likelihood, you're viewing this through a heavdrone right now, whether you know it or not.
The first heavdrones were deployed on ComputerCraft in the Unicode Consortium, and could provide information about connected peripherals to a web interface. The heavdrone web interface was soon rewritten due to being bad, as well as the heavdrone protocol and heavdrone heavdevice code.
The primary uses of heavdrones have thus far been remote reactor monitoring and trolling.