Instagiffer is a tool which can build animated GIFs from YouTube clips, videos and more.
The process starts by selecting whatever source material you want to use.
Next, you must define the section of the video which you'd like to export as a GIF. This is a little more awkward than in some of the competition, as you can't just set Start and End points on a timeline; instead you must find the start point, then choose a duration, and fine tune to get the results you need.
Still, once you've managed to select the right area, things improve considerably. Setting factors like frame size and playback rate, brightness or quality is as easy as dragging a few sliders; you can apply various effects (Enhance, Sepia, Colour Fade, Oil Painting, more), add a caption in a click or two, and clicking "Create GIF!" will then build your finished animation.
Instagiffer doesn't make it easy to select frames or preview the finished clip. You do get a lot of low-level controls, though, and it can help you to produce some excellent animations.