The simplest solution is to download an Android emulator on your computer and run it that way. Something like BlueStacks will let you download ChastiKey from the PlayStore and run it on your computer.
A couple of reasons why it never made it to desktop. It wasn't made with in the typical environment and language where you'd expect to see a web, desktop, and mobile app. I can export to desktop but it would require a lot of redesigning. The main issue with porting it to desktop is not being able to offer emergency keys.
All that aside there are new versions of the app being developed by the community right now where more platform options would be available.
See my recent announcement here:
https://www.chastikeyforums.com/chastikey-chat/future-of-chastikey/