Massive variability searches initiated the design of HAT (Hungarian Automated Telescope), an autonomous observatory. HAT consists of a horseshoe mount similar to the one used in the Automated All Sky Survey (ASAS, Pojmański 1997), a clamshell dome with various utilities, a telephoto lens and a CCD. Expensive hardware elements have been substituted by software running under Realtime Linux: a multitask operating system which can handle processes in real time. A virtual observer – modeled as a finite state machine – is responsible for managing the observatory. The modular structure allows of running virtually any kind of observing program for small telescopes. We describe technical aspects, as well as present test results carried out by HAT1 (Budapest).