Our hosts at Tricycle Developments have created PredictionBook.com, which lets you make predictions and then track your calibration - see whether things you assigned a 70% probability happen 7 times out of 10.
The major challenge with a tool like this is (a) coming up with good short-term predictions to track (b) maintaining your will to keep on tracking yourself even if the results are discouraging, as they probably will be.
I think the main motivation to actually use it, would be rationalists challenging each other to put a prediction on the record and track the results - I'm going to try to remember to do this the next time Michael Vassar says "X%" and I assign a different probability. (Vassar would have won quite a few points for his superior predictions of Singularity Summit 2009 attendance - I was pessimistic, Vassar was accurate.)
I just signed up and did a bunch of predictions. Here are my initial impressions:
A tool like PB is like spaced repetition flash card programs or writing Wikipedia articles - a long-term tool. Some benefits appear quickly, yes, but the bulk of the benefits arrive over years or decades. (PB is somewhat like Long Bets.)
As the saying goes, "In the long run, the utility of all non-Free software approaches zero. All non-Free software is a dead end." If I invest time in PB, what guarantee do I have that I will be able to get my data out of PB when* it dies, especially for topics I didn't write? Are you guys going to license the content under a CC license?
(You should do it early, while there still isn't too much content - once Wikipedia got large, it took years and years and a unique one-time exemption by the FSF to liberate its content from the GFDL into a CC license.)
* And it will die eventually. Every site either dies or evolves out of recognition.
** My data is vastly more important to me than the website software. If I had to, I could run a personal PB in just a flat text file, after all.
2) comments are ridiculously constrained. I dunno if you guys were trying for some sort of auto-Twitter compatibility, but it's really annoying. If you need to dump comments on Twitter and they're too long, then just truncate them.
3) I just judged a Michael Jackson-related prediction wrong, with a citation that the predicted event happened in the wrong year. But in the history section, my comment never appeared!
My current workaround is to make a 0 or 50% prediction (wrong/right), explain my reasoning as best as I can in so short a space, and then separately mark it wrong/right. This is unfair to my score, since obviously I can choose 0 or 100% and always be right.
4) The black boxes on prediction pages (eg. "Join this prediction") are horrible. I was convinced for the longest time that they were buttons to push, and that they were disabled by some JavaScript pokery until I went and read the page source.
5) Newlines in comments do not get translated to a space or two in the comment; they get translated to nothing whatsoever.
6) No apparent way to edit 'due dates' for predictions; many unjudged predictions can't be judged at all because they seem to have been created expired.
7) On userpages, the most recent prediction/action gets split in half by the statistics graph in my Firefox; screenshot.
8) Years get interpreted badly. '2029' becomes - somehow - 2 hours from right now, as opposed to 19 years. screenshot
9) The in-browser JS date checker seems to be quite inaccurate. I've been entering all my dates as '1 January 2024' and the like, which it has never validated - but which turn into the right date when actually submitted.
10) The site is slow. And it seems to be on the server itself. I'm the only user right now, and yet predictions can take as much as 10 seconds to enter. I don't understand how it can be so slow, given that a prediction is a 4-tuple of (date,prediction,owner, user-confidence) which probably adds up to less than a kilobyte of data.
It's our intention to Open Source the PredictionBook code… and has been for at least six months, but we keep not quite getting around to it. It's also my intention to write a top level post about why I think PBook isn't getting much traffic (it being slow is only one reason).
Any one with a reputation on this site that wants access to the code before we get it open sourced is welcome to contact me directly. The code's on github.com and is written in Ruby on Rails.
(gwern, if you want access send me your promise that you'll behave responsibly and your github username.)