This is dmi_browser, a DMI file viewer in your browser.
.dmi files are used by the BYOND platform to store sprites. They are PNG files with extra metadata in a zTXt chunk. That metadata allows the BYOND platform to properly slice the PNG sprite sheet, and to arrange the individual frames into animations. dmi_browser displays individual frames of the sprite sheet, and animates the sprites marked for animations.
If you need some DMI files to try it, you can check out Baystation 12's icon files. Baystation 12 is an open source game for the BYOND platform.
For information about licenses of dmi_browser and libraries incorporated in it, see licenses.html.