There are 2 repositories under bitmap-index topic.
Rust library implementing xor-filters
Cuckoo Index: A Lightweight Secondary Index Structure
A Bitmap library (think BitArray, BitVector32, or Bit Index, not bmp) written in C# with more functionality than the .NET default.
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Distributed bitmap indexing and querying
A RDBMS with bitmap index support simulation with Java.
Useful operations for bitmap indexes and run-length encoded bitmaps.