As Miguel already mentionend in his blog on February 1st:
Peter Sestoft released version 1.0 of his C5 generics library for C#, it is available here:C5 provides functionality and data structures not provided by the standard .Net System.Collections.Generic namespace, such as tree data structures, heap based priority queues and hash indexed array lists and linked lists, making it more comprehensive than collection class libraries on similar platforms, such as Java. Unlike many other collection class libraries, C5 is designed with a strict policy of supporting "code to interface not implementation".
Importing this version into Mono SVN was a real challenge since it exposed many bugs in GMCS and the runtime. Now, over a month later, I finally had the time to fix all these bugs and I'm really happy that we now have a working C5 in Mono SVN again :-)
Today, version 1.0 of C5 has finally hit Mono SVN in HEAD and the 1.1.13 branch.