What viewers can play gif animated images?

You can you use nearly any web-browser, as they should play gifs just fine.

If you'd like to avoid dependencies, you might also consider sxiv. It can play animated gifs using the -a flag, and only depends on imlib2.

Gwenview, as I said, but that's not what I wanted.

gThumb can do it. It comes with few dependencies but looks alien in Fluxbox.

A less desktop-dependent solution is #2 under here:

Install gifsicle.

Create a desktop file:

[Desktop Entry]
Name=GIFview 
Exec=gifview -a %f
Icon=gif
Terminal=false
Type=Application
StartupNotify=true
NoDisplay=true
MimeType=image/gif

and put it into ~/.local/share/applications.