Sailfish Question:

Sailfish will be able to run most applications that were originally developed for MeeGo and Android, in addition to native Sailfish applications. This will give it a large catalogue of available apps on launch.

Considering upon Jolla's declarations that Sailfish OS is be able to use software from following platforms

Sailfish (natively created + ported like from Qt, Symbian, MeeGo - developers have reported that porting a Qt written software with Sailfish SDK takes a few hours only)
Android applications are directly running in Sailfish OS. They are compatible as they are in third-party Android stores, with no needed modification (in most cases).
MeeGo (because of backward compatibility thanks to MeeGo code legacy included in the Mer core)
Unix and Linux (as Sailfish is Linux then using such a software is possible, especially RPM packages, either in terminal/console mode or with limitations implying from using Sailfish UI, if not ported and adjusted)
HTML5