ContrAlto is a full featured software emulation of the historical Alto computer system developed by XEROX® PARC®. This emulator was developed strictly for research and non-commercial use by the Living Computer Museum. The original Alto documentation and schematics were used to engineer the emulator from the “ground up.” Additionally, no previously produced emulation software was referenced or utilized. No Alto compatible software is included with this release, although it may be available from other sources. Original Alto source code is available from the Computer History Museum Archive. The Alto Users Handbook may also be available from other sources.