What I understood (written here http://sfietkonstantin.wordpress.com...lla-summary-2/)

Mer core and the Mer project

Mer (or the mer project) was created after MeeGo was abandonned, first by Nokia, and then by Intel, that “continued” MeeGo with Samsung, by creating Tizen. The creators of Mer wanted to have a meritocratic approach, that is both transparent, and fair, and didn’t wanted to reproduce the errors in the MeeGo project (one of these points was the lack of transparency). Mer means MeeGo reconstructed, and is a complete rebuild of the old project into some core components (“software packages”).

Mer did not provide any user interface. Instead, it tries to be an universal base for those (companies or hackers) that wanted to build, or hack on mobile Linux devices. In order to build an OS from Mer, only two more components are needed, that are the user interface, and the adaptation layers (kernel, hardware drivers etc.) All other components, that are the package manager, basic libraries, kernel etc. are already provided.

Although Mer do not provide user interface, it provides toolkits for building them. For instance the X display manager, that is helped by Qt, is provided to help developing quickly UIs.

Mer is opensource and everybody can contribute to it. Both KDE and Jolla are contributing back to the project.

The Sailfish platform

Yesterday, Jolla announced the creation of the Sailfish platform. Although no much informations were given on this platform, I can guess that it is a more complete platform.

The Sailfish platform seems to be made for OEM that wants a fully complete solution for their device. Since that inside the alliance there are chip makers, the harware adaptation layer should be present. Some helpers about UI, and additional components, for example those used to build app-stores might also be present.

UI do not seems to be shipped, since UI is a great factor of differenciation between manufacturers. While UI is not shipped, both Mer, and maybe also Sailfish will ship helpers, that make the developement of a complete user experience even easier.

Sailfish might or might not be opensourced, but is mostly made of opensource components, like Mer and Qt.

Jolla OS

Jolla Os will be the first incarnation of an OS based on the Sailfish platform. It will integrate Jolla user experience and Jolla services. The system seems to be closed-source, but Jolla said that they might open as much as possible the device.