Fly! II is a sequel to the flight simulator Fly!.
While it had a promising flight model and a unique approach to the cockpit panel system, the lacking default scenery and program bugs kept the simulator from reaching the same level of popularity as Microsoft Flight Simulator. Nevertheless Fly! II gained a steady fan base which can be attested to by the fact that fan add-ons for the simulator are still being created on a regular basis.
The scenery in Fly! II is limited to a few detailed areas with the remainder of the world generically rendered. The result is missing rivers, roads and other visual references that would be used for VFR flights.
The aircraft instrument panels are generally acknowledged to be the strongest feature of Fly! II. The panels are quite a bit larger than those in similar flight sims and require scrolling to view in their entirety. This leads to very detailed and easy to read panels, but also a strange visual effect when the panel scrolls but the outside view does not.
Source: Wikipedia, "Fly! II", available under the CC-BY-SA License.