The Software Botany Sunlight project is a search framework built using Word Aligned Hybrid Bit Vectors. Its sole purpose is to provide high performance in-memory searching of data using unknown combinations of indices. It is developed with .NET 4.0 using C#. The core of this project, Word Aligned Hybrid Bit Vectors, is best explained at this website FastBit An Efficient Compressed Bitmap Index Technology. In addition to implementing Word Aligned Hybrid Bit Vectors, this project layers on Catalogs (bitmap indices) and an entire Search Engine API.
WAH is protected by United States Patent 6831575 "Word aligned bitmap compression method, data structure, and apparatus". However, FastBit is distributed under the LGPL (and so is Sunlight), which has explicit language covering patents and royalty-free distribution in the preamble and section 11. It is my understanding that derivative works are safe from patent infringement so long as they also follow the LGPL. I am not a lawyer, and I do not know if you can use this library commercially. USE AT YOUR OWN RISK