Windows/Mac/Linux (all platforms with Java): Desktop application Shape Collage creates customised photo collages with advanced options that will have you creating fun posters in seconds. Using the application is as simple as dragging your photos into the left-hand pane, and clicking the Create button to generate a new collage. The options can be tweaked to change the collage to any size, shape, or spacing—you can even draw your own custom shape. Once you've generated the collage, they can be saved to JPG, PNG or PSD file—with no watermarks anywhere, making this an excellent software for creating your next poster or wallpaper. Shape Collage is a free download, works wherever the Java platform does. For a web-based application that creates collages from your Flickr photos, check out previously mentioned Collagr.