App: Union
Developer: Fernando Fernandes
Genres: Dienst­programme, Grafik und Design

Union is a free menu bar app that makes it easy to combine multiple images into one.

 - After installing and launching the app, activate it by clicking on its icon at top right, next to the clock;
 - Drag and drop images into it and press the "preview button" at the top left;
 - The native "Preview" app will display the final result -- which is now available for editing / saving / sharing.

Terms and conditions: http://www.backslash-f.com/apps/union/mac/tos.html

Release notes:
Union is now a FREE app. Enjoy!