If you have a minimal light source, even a desklight or something, there are quite a lot of possibilities.
As John pointed out mosses are great, outdoors they don't need a lot of light, indoors however they do require some sort of artificial lightning to thrive. Java moss is an option, but there are other species you could use. In most cases just check your backyard or nearby parc.
Also, strictly not a moss, but perhaps Selaginella uncinata is something for you?
As you said yourself, ferns will also work great. They do well in shaded areas and only require a moist and slightly accidic soil.
You could also add some grasses from the acorus genus. Acorus gramineus for example. Or maybe Ophiopogon japonicus, which is another type of grass.