All my servers has disappeared from the list?

Most likely the API-key has expired. Under the hood Laravel Forge uses Laravel Passport for creating the API-keys. The default lifetime is one year. The lifetime of the API-key will change to 10 years in the future.

What language is F-Bar written in?

It’s written in Swift. Read more here

On how many computers can install F-Bar with the same license

You can install F-Bar on three computers at the same time. One a work, home and on you MacBook is just fine.