Translation:While you are here, I will stay.
The future subjunctive expresses doubt about whether a specific future action will take place. It is introduced by adverbial clauses beginning with se, quando, enquanto, logo que, etc.
No, that's simply wrong *, which is quite disappointing in a tool that many people trust. Anyway, here's another opinion: http://www.conjuga-me.net/verbo-estar
* It turns out Verbix already know about this error (and a similar problem with the conjugation of "dar") - see the feedback page here: http://wiki.verbix.com/Verbix/Verbix2008Feedback
It's the future subjunctive tense. http://www.learn-portuguese-with-rafa.com/future-subjunctive.html