YS Flight Simulation System 2000 is a fully featured lightweight flight simulator. As well as basic functionalities, it has network feature that allows you to fly with or against your friends. You also can fly a formation leader, dogfight, intercept, attack ground, take off and land on an aircraft carrier, etc., you can choose your airplane from more than 50 airplanes, and there are several maps as well.
The graphics does not look as good as recent flight simulators, but YSFLIGHT does not require expensive hardware; you donīt have to worry about the speed of your PC when you play over the network (You donīt have to ask all of your friends to buy a PC as good yours!).
The archive includes two versions, OpenGL version and Standard version, and if your PC is equipped with a nice graphics card, you can use OpenGL version that gives a little better graphics, or Standard version will run fast without such a nice graphics card but the graphics quality is not as good as the OpenGL version. You can record entire flight, and review your flight later to improve your flight technique.