Despite the name, MortButtons is NOT a tool to assign applications to buttons, like BtnPlus, VITO ButtonMapper, PowerButton, and similar tools. Instead, it allows to create multiple small menus, which can be used with just one button (also see "General Usage" in the manual).
It also offers a menu that consists of all currently running applications, thus enabling a quick and easy task switching like Alt-Tab in Windows. These menus can be assinged to your buttons with either the systems settings or any tool you use (like those told above). Please refer to the manual of your tool for details to those.