Asymptote is a powerful descriptive vector graphics language that provides a natural coordinate-based framework for technical drawing. Labels and equations are typeset with LaTeX, for high-quality PostScript output.
"Academic literature should be freely available: developing countries need access; part time ... thinkers ... journalists and the public can benefit; ... you’ve already paid for much of this stuff with your taxes ... important new ideas from humanity"
EndnoteWeb, RefWorks, Connotea, CiteULike, Zotero, Mendeley. Nice summary of the state of the art by Martin Fenner. Conclusion - not much to choose in some ways - personal preference!
J. Huang, Z. Zhuang, J. Li, and C. Giles. Proceedings of the 2008 International Conference on Web Search and Data Mining, page 107--116. New York, NY, USA, ACM, (2008)