There are applications for deciding on meeting times, and there are applications for converting times across multiple timezones, but it's not clear if there's anything which combines the two (or which uses any kind of rating system for availablility; binary "available / not available" seems to be the default).
I was originally creating it as much to show off Ferreteria as because there appeared to be a legitimate need, due to the fact that most existing meetup apps seem to be assuming that everyone is in the same timezone (probably because it's designed more for IRL meetings than virtual ones).
Since then, other priorities have intruded and I have not had time to work on this.
Action starts with a planned meeting -- that is, a group of people want to meet within some time-frame, there are a number of possible dates and times during which each of them is available, but they don't yet know which of the possibilities is best.
The user who creates the planned meeting may also enter times and dates on which they are available, each optionally rated on a scale from 1 to 10. Other users may then rate each of those t/d combinations as well, or (if the creator allows it) enter their own and rate them as well.
As more users provide their availability information, the application displays the best candidates for actually holding the meeting.