This release of Reversi is mainly just to convert it from being a 32-bit app to a 64-bit app. This means it will be able to run on macOS 10·15 Catalina, which is the first version of macOS to drop support for 32-bit apps. Other than that it should look and behave virtually identically to the previous version.
One side effect of the conversion process is that Reversi now requires Mac OS X 10·7 Lion or later. I don’t anticipate this being much of an issue since that version has been out for 8 years now…