The System.Collections namespace in the .NET Framework provides a number of collection types that are extremely useful for manipulating data in memory. However, some specialized implementations of ISet are not available. Iesi.Collections 4.0 for .Net 4.0 contains the LinkedHashSet (preserves insertion order), the ReadOnlySet and the SynchronizedSet. The latter two wrap an actual set.
Additional ISet<T> implementations for .Net 4.
This library was based on http://www.codeproject.com/Articles/3190/Add-Support-for-quot-Set-quot-Collections-to-NET,
but the version for .NET 4 is significantly different, since ISet<T> is now available in the framework itself.