It might help to know what capabilities you are looking for in a simulator. Kinematics, dynamics, sensor models, validation, real-time vs. non-real-time, graphics, multi-vehicle ...?
The flyer_sim package in starmac-ros-pkg has a very basic simulator implemented as a node written in Python. At present there is a simple nonlinear dynamics and sensor model that is not meant to exactly simulate a particular quadrotor, but rather to simply have 'quadrotor-like' dynamics so that the rest of the system can safely be tested (and learned). In the near future we expect to have more accurate models based on system identification implemented in the flyer_sim package.
While not strictly speaking part of the simulator, the overall package also has a means of visualizing the simulation in rviz (see the end of this tutorial for a screenshot).