Doujin pack: collection of several doujins, all japanese.
Doujin/CG set/etc.: single download for doujin/CG set.
Translated: download for english translation.
(When there are multiple links, they are alternate downloads for the same thing, so download only one, not all.)
Ratings:
Safe: all ages, no nudity.
Ero: partial/full nudity and/or suggestive situations.
Explicit: explicit sexual content.
Alternative: alternative sexual content (tentacles, futanari, heavy BDSM, etc.)
If you find a doujin that isn't listed yet, or a dead link, or a new link for something, please report it in the IRC channel.