Sailfish OS is a Linux-based operating system based on open source projects such as Mer and including a closed source UI. The project is being developed by the Finnish company Jolla.
The OS is shipped with the Jolla smartphone and tablet (the sale stopped in 2016 but devices are still supported with software updates) and from other vendors licensing the OS. The OS is ported by community enthusiasts to third-party mobile devices including smartphones and tablet computers. Sailfish OS can be used for many kinds of devices.
The OS is an evolved continuation of the Linux MeeGo OS previously developed by alliance of Nokia and Intel which itself relies on combined Maemo and Moblin. The MeeGo legacy is contained in the Mer core in about 80% of its code; the Mer name thus expands to MEego Reconstructed. This base is extended by Jolla with a custom user interface and default applications. Jolla and MERproject.org follow a meritocratic system to avoid the mistakes that led to the MeeGo project's then-unanticipated discontinuation.