Less known data structures come to mind: - Topological sort. Great for dependency traversal. - KD-Tree. Great for geo-spatial search. - Consistent Hashing.

Less known data structures come to mind: - Topological sort. Great for dependency traversal. - KD-Tree. Great for geo-spatial search. - Consistent Hashing. Great for scaling and clustering. - Fuzzy Hashing. Great for document digest and mining. Sadly there might be a patent conflict somewhere. - Extendible Hashtable. Amazing space-efficient and extendible lookup table. - Bloom Filter. Space-efficient check.