This release of GridBike, as with the recent release of Reversi, is simply to convert the app from 32-bit to 64-bit. This means it will be able to run on macOS 10.15 onwards (and will stop warnings on macOS 10.13 and 10.14). Other than that it should look and behave the same as the previous version.
One side effect of the conversion is that GridBike now requires macOS 10.7 or later.
I’ve released a new Windows version to match. This is also unchanged apart from being built with a newer version of Visual Studio.