Both software and application software are essential for accomplishing tasks with a digital device. Today, most application software is distributed online or through app stores. The main executable file for PC software has a(n)extension, whereas executable files for Macs have a(n) extension. New versions of software are called and are indicated by version numbers such as 1.0 and 2.0. A software or patch is a small section of program code designed to correct problems and address security vulnerabilities. Software payment models include free, one-time purchase, , trial, and freemium. Software licenses, referred to by the acronym , can be divided into two main categories: public and proprietary. software is typically available directly from the publisher or an app store and may have options for site licenses as well as single-user licenses. Freeware is copyrighted software that is available free of charge. is also available free of charge, but is limited in some way until you pay for it. Open software may be sold or distributed free of charge, but the distribution must include the source code