Rigetti Computing seems to have a very nice system for testing out quantum algorithms. I haven’t tried it out myself yet but it consists of Forest, a cloud-based API with access to up to 26 simulated qubits. There’s also access to 19 real qubits apparently although that’s on request. To go with it, pyQuil is a Python environment that provides a nice way of driving the cloud API and is where the quantum algorithms are defined.
One nice advantage over Microsoft’s Q# is that (as I understand it) qubits in Q# are opaque which means that the state of qubit can only be accessed via measurement whereas in pyQuil the register state can be accessed (using the wavefunction keyword). While this opacity in Q# reflects the reality of a physical quantum processor, a simulator should permit access to the internal state in order to help with understanding what’s going on.
However, both certainly have a role to play in main-streaming quantum computing and helping us all get ready for a time when real quantum processors become as available as GPUs (maybe).