Beryllium's low density, stiffness, corrosion resistance and high melting point make it useful in aerospace applications such as gyroscope rotors and rocket nozzles, and in the domes of tweeters or high-frequency drivers in audiophile loudspeakers.
Beryllium is used as a hardening agent in copper alloys which are formed into tools. Such tools do not spark, which makes them useful when working around flammable or explosive substances. They are not magnetic, which makes them useful when working around operating MRI machines and mines with magnetic detonators.
In bulk form beryllium is harmless. However, the metal dust and compounds are quite toxic, causing a pneumonia-like condition called berylliosis in the lungs of chronically exposed workers.