Perma.cc helps scholars, journals, courts, and others create permanent records of the web sources they cite. Perma.cc is simple, free to use, and is built and supported by libraries. Free to use at 10 records per month, unless you're an academic. Designed specifically so that it can be used for citations. Has an API. Open source. Written in Python, uses Django. Stores things as WARC files.

Github: https://github.com/harvard-lil/perma

A wiki as well as a meta wiki that tries to unify different sources of information for the purposes of scholarship and easy citation. Claims that it goes back to primary sources for its constructions. Offers fact maps and topic trees, among other knowledge structures.