Tenifer and Melonite are trade names for firearm finishing processes that involve salt bath nitriding. The heart of the matter is probably licensing rights rather than technology. I do not have any special inside information, but I believe that Glock will not let the supplier license the Tenifer name to any other firearms manufacturer; therefore, other firearms manufacturers are using a similar finish but from other chemical suppliers or under different tradenames.
Historically, firearm parts were black oxided, which is an oxidation process which is only a few millionths of an inch thick, does not offer much corrosion resistance, and doesn't alter the underlying steel. Salt bath nitriding is a case hardening process that leaves a fairly thick, corrosion resistant, hard surface.