This simple tool lets you view animations while controlling the playback speed for each image that makes up the GIF file.
This program stands out not just for that but also for letting you zoom in or out on any part you want or take screenshots of a particular frame, which you can export as a new image.
Another good thing is that you can save the animation in its original or modified speed, or set the tool as your default application to open GIFs.
If what you're looking for is to personalize your short video clips, 7GIF is the tool for you. It has a very simple interface that allows you to work with no hassle.