From the DataSF website:

DataSF is a central clearinghouse for datasets published by the City & County of San Francisco. The site allows you to find datasets in several ways: general search, tags/keywords, categories, and rating. The goal is to improve access to city data through open machine-readable formats. While the number and quality of datasets is increasing, we recognize there is much more that we can do. You can help by rating and commenting on existing datasets or by telling us what datasets we should make available to the public.

[From DataSF | About]