Conference Management Software

I'm in the need of some conference management software. Preferably something that is available as Open Source. I've found one that is close to what I need, Corga. It however is a little rough around the edges, but I can enhance it since it's open source and I have access to the code. However, I'd like to look at some other alternatives. Here are my requirements:

• Allow presenters to submit abstracts and papers.
• Catagories for the various papers.
• Allow reviewers to rate abstracts.
• Publish a program from the accepted abstracts.
• Allow conference chair to assign reviewers.
• Allow people to register for the conference.
• Control various dates, like when the abstract submissions ends, registration begins, and when registration ends.

Ideally, I would like this all with in one open source application. As I said, Corga is the closest thing I've found that meets most of these needs. The issue with Corga is that it requires a password for each paper, and that presenters have to login in multiple times to submit more than one paper. Anyways, I'd be interested in hearing what other software that people have used, that a non-profit organization could use to run a conference.