There's peacock spiny eels and zigzag spiny eels, both of which are kind of similar to fire eels but smaller.
There's also kuhli loaches - they've got an "eel-like" look about them. They're considerably smaller so they would be good for a small or larger tank. Peacocks and zigzags are some of the smallest spiny eels but they still need a fair amount of space - maybe 50 gallons min? I'm not sure but someone else can verify this probably.