Sailfish is a Linux-based mobile operating system developed by Jolla for use in its upcoming smartphones and can be used for any of mobile devices.
As we all know, MeeGo is a Linux-based free mobile operating system project, primarily targeted at mobile devices and information appliances in the consumer electronics market. Mer is a mobile-oriented software distribution, targeted at hardware vendors to serve as base for Linux-based operating system. It is a fork of MeeGo. Sailfish is based on MeeGo and Mer, use standards established with MeeGo which were used and continued in the Mer. Mer project is the core OS that serves as the base of Sailfish OS.
Sailfish includes a proprietary user interface that Jolla intends to use to differentiate its smartphones from others and as a competitive advantage against devices that run Google's Android or Apple's iOS.
Mobile phone manufacturers (e.g. Nokia, Samsung, etc.) will be able to license and use Sailfish on a phone, similarly like Android, in fact the whole Sailfish OS is to be licensed as the open source.
Sailfish will be compatible with Android apps thanks to built in Alien Dalvik layer from Myriad Group, known from running Android apps. Many Android applications will run on Jolla devices unchanged. Jolla's Sailfish OS works in a tablet too.
Although Sailfish has been presented first for mobile use with upcoming smartphones by Jolla, it is also OS for general purposes and devices like smart television, computers, laptops, netbooks,tablets, navigations, cameras, household devices of many kinds, for automotive in cars and IVI, for sailing purposes in yachts and boats, and others.