QuEST

A high performance simulator of quantum circuits, state-vectors, and density matrices. It achieves speed through multithreading, GPU acceleration and distribution, running efficiently on laptops, desktops, and networked supercomputers. The toolkit just works; it is stand-alone, requires no installation, and is trivial to compile and get running.

It is simple to use and integrate:

• Supports over 140 operations, from basic gates to complex esoteric operators, many with bespoke algorithms for efficiency. Also supports general user-specified unitaries and decoherence channels.
• Includes comprehensive documentation with mathematical descriptions, circuit diagrams, error handling details, and links to source code.
• Uses a rigorous set of unit tests run after each code change, often trying every possible input combination against analytic results.
• Has no external dependencies and compiles natively on Windows, Linux, and MacOS, enabling deployment on various hardware.
• Provides fast low-level access to data structures, support for different numerical precisions, and utilities for error redirection, making it useful for integration into larger software stacks.

It is available under a permissive license and is free and open-source.