Socrato is a Massachusetts-based company bringing test preparation materials online so they can be distributed and used more effectively.
The team behind Socrato started off by loading all of the site's content manually, including sample questions for the SAT and Massachusetts state tests. Realizing that it would be much easier grow its collection by crowdsourcing, it has built a user generated content system that teachers and academic coaches everywhere can use to upload their own materials.
Most of Socrato's tests consist of multiple choice, fill in the blank, and true/false questions. Long essay support is not quite there yet but will be added in the future. Users who want to add tests can do so by uploading PDF, Word, PowerPoint, and other files as complimentary materials. Teachers who want to distribute test prep materials to a particular classes can also set up groups on Socrato for that purpose.
Socrato isn't supposed to be used to actually administer tests (although I would really like to see it evolve to that point because it would be much more powerful). Rather, students can take the practice tests on the site and it will tell them how well they did and where they need to improve. The service is smart enough to tell which subjects students did well on, and in the next release it will even be able to track how students deliberate on questions by analyzing which answers they cross off first.
This site needs some work in terms of its user interface and the ease with which users can add tests. But I think it's a great idea to bring more educational resources online.