A new state-of-the-art resource sharing software has been in the works at Equinox (with sponsorship from ohioNET) for some time now. And while it isn't ready for download, it did cross a new threshold recently. As of August 2, 2010, FulfILLment was established as its own open source project (as opposed to a piece of Evergreen).
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Equinox has been talking about it for quite some time but there appears to be actual movement on a true open source ILL module for linking not just open source library systems but all ILS products (pending some standards compliance issues I imagein).
The name of the product is FulfILLment and the website says "it will provide library users seamless access to materials owned by libraries using FullfILLment—no matter which integrated library system his or her library uses."