The team behind the open source Zotero citation management software has been actively developing “sync” functionality for quite some time now. It allows you to work with your references collection from multiple computers by storing the latest copy of your collection on the Zotero servers.
An optional part of the sync system allows you to store PDF files and such like in your collection (full-text copies of papers etc.). Zotero provides 100MB of storage free to everyone, but towards the end of 2009 they introduced an optional premium service, in conjuction with Digital Scholar.
For an annual fee, you can expand your storage space. I’ve opted for 1GB which costs me US$20 per year. Other suggested quantities are 5GB for US$60 per year, or 10GB for US$100 per year. Other arrangements can be made by special request.
It is important to note that Zotero itself is (and always will be) free software. Additionally, the basic sync process (the ‘metadata’ part which describes your reference collection) is free too… and that’s all a lot of people need. For the cash-strapped researchers among us, you can hook-up your Zotero installation to any server which supports WebDAV. That means you can run your own server, or subscribe to a cheaper online storage provider.
The payment you make to Zotero is for maintaining the storage requirements, and for ensuring that the integration between Zotero and Digital Scholar is as reliable as it can be. As far as open source business models go, I think this is a great one. I am more than happy to pay for the benefits this arrangement provides. It is a much-appreciated valuable service for an excellent piece of open source software. And it is probably much more financially sustainable for the Zotero devs than a simple “pay once” retail concept would be.
Although I do hope they sort of the sync delays sometime soon… 😀