Descargar is not an application-creating company; instead, the verb "descargar" is the Spanish word for "download." Thus, the word "descargar" in the context of an app means to download and install it to a mobile or desktop computing device.
The phrase "descargar para" followed by an operating system name asks for downloadable software for that specific OS. Although a wide variety of applications are supported by all device types, some apps are specifically released only to one.
Applications that are "descargar gratis" are free to download to a device. Device operating systems such as Android, iOS, Blackberry and Windows each maintain updated lists of the most popular free and paid apps. Social media apps such as Facebook, Facebook Messenger and Twitter consistently rank in the most popular free applications downloaded by users, as of 2015. Other free apps that rank highly include video software such as Youtube and Netflix, photo apps including Instagram, and music radio programs such as Pandora and Spotify.
Other meanings for the verb "descargar" include to unload, to discharge and to fire, as with a weapon. The word comes from the late Latin term "discarricare," a form of the term "discarrico," meaning "to unload." This etymology in turn traces back to the base Latin verb "carrus," which means "to load."