After working on it off and on for two years, I have released the final version of "Rabbit Sheets - Rabbit Database and Pedigree Generator." Its advantages are that it is free, simple, and can be used anywhere with mobile devices. Its major disadvantage is that Google Sheets has some annoying lag while entering data.
I won't be making any more improvements on Rabbit Sheets. Instead, I am going to start working on a PHP/MySQL rabbitry management application. I can do things with PHP that are rather difficult or impossible to accomplish with Google Sheets, because Google Sheets is not intended to be anything more than a spreadsheet.