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.
It is based on MeeGo and Mer, use standards established with MeeGo which were used and continued in the Mer, like eg. API. Mer project is the core OS that serves as the base of Sailfish OS. It provides a functional core Linux stack that boots up to the screen but without any UI and without any hardware adaptation eg. Mer does not have system kernel. Nemo provides a functional UI framework and it has its own UI and application set that are compatible with Sailfish. However Nemo applications are not at the moment included in Sailfish OS and the UI is radically different. The Sailfish OS and the Sailfish SDK are based on the core and tools of the Mer operating system core, which is a revival of the core of the MeeGo project of Nokia, Intel, and Linux Foundation among others. Sailfish includes a multi-tasking user interface that Jolla intends to use to differentiate its smartphones