To make a comprehensive, fully-featured, and extendable go problem resource.
The Problem Solver
A Java applet that lets you interactively solve go problems. Multiple paths, both correct and incorrect, can be followed in an attempt to solve a problem. You can view the solution as a numbered sequence, an animation, or you can navigate it with colored paths. The problem solver can display several kinds of Smart Go File markup, including marked stones and intersections, and comments.
Stores go problems of varying types. Searchable and extendable. Problems are rated with two types of difficulty measurements, as well as a user-rated "coolness" factor.
goproblems.com measures two types of difficulty. Since it's hard for people to objectively measure the difficulty of a problem, goproblems.com measures two statistics that independently or in small numbers mean little, but over time and in context should provide a means to measure the difficulty of a problem.
When you're playing with a problem, you'll see the difficulty expressed as: x/y. x is the percentage of people who've gotten this problem wrong. y is the average number of seconds it took people to solve the problem correctly.
To give people a way to objectively rate problems, they can vote on coolness. Ten is the most, one the least. The coolness factor of a problem is the average of the votes.
What if you don't agree with the answer of a problem? Or you think there's a cleaner way to achieve it? Well, just add a comment. This is the best way to provide feedback, and also just to discuss problems, especially those of the "find the best move" variety. The comment button doesn't show up until you've tried the problem, as comments might contain spoilers.
How it Works
Users are given Elo ratings. Every problem attempt pits a user's Elo rating against a problem's Elo rating, and both are adjusted. The adjustement depends somewhat on how stable a rating is, which mostly means how many data points we have. These Elo ratings are converted into Kyu/Dan ratings with a basic heuristic.