The Northrop F-20 Tigershark (initially F-5G) was a privately-financed light fighter, designed and built by Northrop. Its development began in 1975 as a further evolution of Northrop's F-5E Tiger II, featuring a new engine that greatly improved overall performance, and a modern avionics suite including a powerful and flexible radar. Compared with the F-5E, the F-20 was much faster, gained beyond visual range air-to-air capability, and had a full suite of air-to-ground modes capable of firing most U.S. weapons. With these improved capabilities, the F-20 became competitive with contemporary fighter designs such as the General Dynamics F-16 Fighting Falcon, but was much less expensive to purchase and operate.
Much of the F-20's development was carried out under a U.S. Department of Defense (DoD) project called "FX", intended to sell less-advanced fighters to allies to limit the possibility of front-line U.S. technology falling into Soviet hands. FX was a result of changes in military export policy under the Carter administration in 1977. Northrop had high hopes for the F-20 in the international market, however policy changes following Ronald Reagan's election meant the F-20 had to compete for sales against aircraft like the F-16. The development program was eventually abandoned in 1986 after three prototypes had been built and a fourth partially completed.
Source: Wikipedia, "Northrop F-20 Tigershark", available under the CC-BY-SA License.