C# implementations of radix trees, or space-optimised tries (see the Wikipedia article).
Radixtree.NET provides multiple radix-tree implementations for different use cases:
Implements ISet<string>
Implements IDictionary<string, T>
Implements IDictionary<string, T> and is thread-safe
The predecessor to this library was initially developed at Majako for use in nopCommerce to efficiently handle cache keys.