A starter index of the quantum software ecosystem. Each entry below is a jumping-off point — vendor docs are usually the most current source of truth.

General-purpose SDKs

• Qiskit — IBM’s Python SDK; circuits, transpiler, primitives, and access to IBM Quantum hardware.
• Cirq — Google’s Python framework, geared toward NISQ experiments and gate-level control.
• PennyLane — Xanadu’s hybrid quantum/ML framework with autodiff across many backends.
• Q# — Microsoft’s quantum programming language with Azure Quantum integration.

Simulators

• Stim — Extremely fast Clifford and stabilizer simulator; the standard for QEC research.
• QuEST — High-performance multi-threaded / GPU statevector and density-matrix simulator (C / Python).
• Qulacs — Fast C++ statevector simulator with Python bindings.

Domain-specific

• OpenFermion — Fermionic operators and electronic-structure tooling.
• Mitiq — Error mitigation toolkit (ZNE, PEC, CDR, …) from the Unitary Foundation.
• TensorNetwork — Tensor network contractions for classical simulation of quantum circuits.

Stub — expand with personal notes, gotchas, and version pins as you use these.