It's a free online image maker that allows you to add custom resizable text to images. It operates in HTML5 canvas, so your images are created instantly on your own device. Most commonly, people use the generator to add text captions to established memes , so technically it's more of a meme "captioner" than a meme maker.
Good luck trying to figure out where your favorite GIFs originated. Whoever created the original video usually isn't the same person who GIF-ed it. And people rarely include proper attribution, so they're difficult to accurately source.