Analysis Situs is open-source, extensible software that assists in the development of CAD geometric algorithms based on Boundary Representation (B-Rep) data structures. The software is coupled with OpenCascade library which is an open-source geometric modeling kernel offering a broad range of modeling operators for the development of multipurpose CAD systems and utilities. Analysis Situs serves as a framework for constructing geometric modeling algorithms. Additionally, Analysis Situs offers some advanced facilities for inspection of geometric and topological structures of existing CAD parts (hence the name "Analysis Situs") which can be imported from any popular CAD system.