Nope.. can't fit an eel in there. Can't really fit a fish of any kind in there.
You MIGHT be able to house a shrimp or small snail in there but in all honesty it is not really a suitable set up for anything living.
A good use for it could be to put a little soil covered with sand in it and put some plants in it. Sit it by a window sill and the plants will grow really nicely... it could be a little plant nursery if you want to plant your tanks.
Another use could be picture tank. I have a half gallon tank that I have divided and use to take pictures of my bettas so I can get better light and get them to flare easier.