It's called 'rat' on FIBS and should be alive most of the time. To use it, just talk to it. For example, if your rating is 1500 and your opponent's rating is 1700, and you're playing a 3pt match, type:
tell rat 1500,1700,3
It'll tell you how many points you'll win or lose, and also what the probability is of the underdog (lower rated player) winning the match.
Note that your rating comes first. You must also use commas to separate the numbers. Note also that at the moment it doesn't take players' experience into account; it assumes both players have experience of 400 or over (i.e. when experience ceases to have a special affect on ratings changes).
I'll make it a little easier to use, when I have time, so that you can type things like:
tell rat Ivan,5
Which will look up the rating and experience of you and your opponent (in this case, Ivan). Also:
tell rat ratings
Which will tell you the ratings changes for the match you're currently playing.
tell rat -3 -5
It will give you the leader's chance of winning the match, from Kit Woolsey's match equity table. In this case, the leader (you) should win the match 66% of the time. The table is used with Kit's permission. Note: it doesn't matter in which order you give the scores - rat will always give the leader's match winning chances.
rat doesn't respond to tells it can't parse, and it doesn't even see messages left for it with the 'message' command.