In the past, all astronomical software had built-in custom drivers, written especially for that application to talk to particular models of telescopes, focusers, etc. If your equipment was not supported with a particular program, you could not connect it. Even worse, if you wanted two or more programs to share the same telescope, it could not be done. With the advent of ASCOM, all of this has changed.
The AStronomy Common Object Model (ASCOM) is a standardized interface for communicating with astronomical equipment. Standardized interfaces allow applications to talk to hardware without having to be customized for the particular command set of each device. As part of this effort, a set of mostly open-source drivers have been made available via the ASCOM Platform. Driver standards currently exist for telescopes, domes, focusers, cameras, and filter wheels.
Applications may also communicate using interfaces that conform to the ASCOM General Requirements, without conforming to a particular standardized interface. MaxIm DL uses both types of ASCOM compatible interfaces.
The ASCOM Platform, available from http://ascom-standards.org/, provides the basic components required to run ASCOM drivers. Many of these components are open source, and all are free. In addition, many ASCOM drivers are available through the web site, either directly or through links to third-party manufacturer sites.
ASCOM drivers are available for a large variety of equipment, including telescopes, focusers, dome controllers, rotators, cameras, and filter wheels. In addition, it is possible to connect through ASCOM interfaces to a number of other software programs. As an example, telescope interfaces can be chained together using the POTH Hub or similar program to allowed shared access to a telescope.