An idea how to let users choose which utility they want to use for which format... and how you could maybe simplify RAR installation for less-techie users

Maybe in Preferences you could have a tab "Archive formats" with a table view where users could select which formats they want to appear in Keka's drop-down menu for compression... so if someone doesn't need support for some format, to allow him to hide it from the drop-down menu... and for formats that are supported by multiple utilities, you can add a drop-down menu next to that format in that table-view in preferences for them to select which utility they want to use for it.

And you can have RAR on that list... and if the user checks the checkbox next to it and RAR isn't installed, Keka could show a dialog with a link to the download page for RAR and tell the user to drag & drop the archive after downloading it to Keka's window... and if RAR isn't installed and the user drags & drops that archive to Keka's window, Keka could recognize the contents of that archive and show a dialog "Would you like to install RAR from this archive?" and if they click "Yes" Keka could copy the contents of that archive to it's Application Support folder (so you can keep Keka sandboxed and without having to ask users to copy it somewhere manually) and use it from there... and maybe if they decide not to use RAR anymore, if they uncheck that checkbox Keka could just remove it.

Also... it would be good to have a table view for users to select which formats they want to be associated with Keka for unarchiving.