YSFlight is a low-key flight simulator made by Soji Yamakawa, a.k.a. Captain YS. Originally released in 1998, YSFlight has been continuously updated through the years with several beta and a stable release each year. On his website, Mr. Yamakawa has a full development log.
The key features for YSFlight revolve around the following points:
There are a wide variety of low-polygon stock aircraft, however there are thousands of other aircraft and addons to download and expand your flight experience.