Online GIF optimizer
You can also use: http://ezgif.com/optimize?url=http://link/to/image.gif
This tool is designed to shrink gif file size by reducing the number of colors in each frame.
Each gif frame can use up to 256 unique colors, and by reducing this number, you can achieve a smaller file size.
It makes multiple variations of your input image, and you can choose the one that has the best size/quality ratio for your needs.
Lossy GIF compression
Compresses GIF with Lossy GIF encoder which implements lossy LZW compression.
It can reduce animated GIF file size by 30%—50% at a cost of some dithering/noise.
Remove every n frame
The frame drop option can remove every second, third, or fourth frame to reduce frame rate and, therefore, file size. Useful for gifs with a high frame rate.
This option makes some unchanging parts of the frames transparent.
The results heavily depends on the nature of the image. It may give huge file size reduction in some cases when images have large, static areas. Likely will give poor results for converted videos. The fuzz factor represents how similar colors can be considered as equal.