For testing simple algorithms, you might be able to get by with a 2D simulator. There are a few out there that I am aware of:
- Stage: http://playerstage.sourceforge.net/index.php?src=stage
- STDR: http://stdr-simulator-ros-pkg.github.io/
Stage is an older, but useful, simulator which has integration with ROS (http: //wiki.ros.org/stage_ros) which will allow you to write code to interact with and manipulate robots in C++/Python.
STDR is a newer 2D simulator which also has ROS bindings.
If you want a full 3D simulator I can think of three, which again are not AI or quadrotors specific, that might meet your needs:
- Gazebo: http://gazebosim.org/
- MORSE: http://www.openrobots.org/wiki/morse/https://www.openrobots.org/wiki/morse/
- V-REP: http://www.coppeliarobotics.com/
Gazebo is the 3D counter part to Stage and has ROS support, and it has been used with quadrotors (http://www.ros.org/news/2012/03/announcement-of-hector-quadrotor-stack.html), though it has no out-of-the-box support for them.
MORSE is based on blender and its game engine, it has ROS and YARP and Raw socket support.
V-REP is a free for education simulator with support for many languages and platforms, including Windows and C#, if that is your kind of thing.