ArmaLite's first success came shortly after it was founded with the introduction of the AR-5, a survival rifle chambered for the .22 Hornet cartridge. The AR-5 (AR stands for ArmaLite) was adopted as a U.S. Air Force as the MA-1 Survival Rifle.
In 1954 Eugene Stoner became Chief Engineer at ArmaLite. Stoner was a Marine in World War II and an expert with small arms. His design for the AR-10 assault rifle was entered into the U.S. Army trials in 1955 as a possible replacement to the venerable yet outdated M1 Garand. It met stiff competition as it was pitted against the Springfield Armory T-44, and updated M1 Garand design that became the M-14, and the T-48, a version of the famous Belgian FAL rifle. The AR-10 lost the trials to the T-44, mainly due to the AR-10's unorthadox appearance and configuration.
The famous AR-15 rifle was developed as a smaller version of the AR-10. Both designs were liscensed to Colt in early 1959. You can read more about the AR-15 at the M-16 article. With both the AR-10 and AR-15 designs sold to Colt, ArmaLite was left without a viable product. So, in 1963, development began on the AR-18 assault rifle, an "improved" AR-15 with a new gas system that did not violate the Colt held patents. The AR-18 is an excellent rifle, but it did not gain any military support. It is most famous for being adopted by IRA terrorists in Ireland, who dubbed the rifle "The Widowmaker." The AR-18 did serve as the basis for the current British assault rifle known as the L85, which is essentially an AR-18 in bullpup configuration. Other designs, such as the Singapore SAR-80 and German G36, are based upon the AR-18. ArmaLite has changed hands a number of times throughout its history and most recently was reorganized in 1995. Today, ArmaLite produces a number of AR-15 and AR-10 based rifles, as well as 50 BMG rifles.
For more information: http://www.armalite.com/