Unlike Ubuntu, Sailfish uses the conventional middleware stack from Mer (i.e. graphics wise it's Xorg with plan to move to Wayland). Applications wise I can't really yet compare, since there aren't much details on Sailfish before it will be published. Hopefully it will be open sourced together after the launch (I mean the default applications like e-mail client and the rest). Silica UI components are open source already.
See https://sailfishos.org/about.html
See also: https://wiki.merproject.org/wiki/Main_Page