Telescope or astronomy devices control
There are nearly as many different astronomical set-ups as astronomers. Lots of devices are required in a set-up, and many of each type exist. Many are not supported by free software. A hardware compatibility list is being done here.
Acquisition software generally have to handle high-end cameras, DLSR and focusers. Autoguiding software generally have to handle low-end cameras and telescope motorisations, possibly focusers too. They make very different tasks and address a large range of devices.
Some projects do not focus only on one particular device or even type of device, and provide abstraction layers or even try to standardize the way astronomical programs communicate with each other and with devices. INDI is such a project.