Cross-platform citation/manuscript management software for academics

Question

I'm an academic looking for a software to manage my PDF files with the following capabilities:

1. Organize into folders by topic, read/unread, etc.
2. Annotations
3. Mac/iPad/iPhone platform
4. Can be used for citation management

So far I see two contenders: Mendeley and Papers - however Mendeley doesn't allow for (2) and (4) and although Papers does everything, I have to buy separate licenses for each device which is expensive and annoying.

Am I missing some other option?

Answer 1

Have you considered using Zotero? From their website:

Zotero [zoh-TAIR-oh] is a free, easy-to-use tool to help you collect, organize, cite, and share your research sources.

It allows you to store bibliographic information and PDF's of research papers, produce bibliographies and citations, and share your bibliographic data with other users. It seems to cover everything that the OP asked for.