NengoCalc 4.1 for Mac is available as a free download on our software library. The application is included in Productivity Tools. This free Mac app is a product of SilentMountain.
From the developer:
With this tool, the user can convert Japanese dates into Western equivalents. NengoCalc uses a comprehensive database of chronologcial data and era names to accomplish the calculation of the Western dates. The main algorithms and tables are derived from Tsuchihashi.
You may want to check out more Mac applications, such as CalaMatic Scientific Calculator or UltiCalc 3, which might be similar to NengoCalc.