Horizon is a BBC Model B emulator for Mac OS X.
Horizon (formerly MacBeebEm) was one of the first emulators available for Mac. Despite this, it has fairly good compatibility with original BBC software, allowing you to play titles such as Elite without problems. The Mac OS X version adds an improved GUI and significantly improved sound to the original version.
What's new in Horizon
Updated to shell version 2.3. See "About the Shell" for changes.
Fixed bug whereby dropping file into Horizon window would cause an assertion failure.