Folded pens! Yes
The MOST fun is to just go out into the backyard and pick up a bunch of random twigs. The ones that make the best (imo) marks are the ones that are frayed or knobby at the business end, so that they release your ink in unexpected ways. You can get marvy marks using twigs.
-- feathers (dip the feathery end in the ink and go at the paper using different angles, to get thin wispy marks and then very wide wet marks
-- use green leaves, like the green tuft on the top of a carrot (you could bind it with a make-shift ferrule, like a rubber band, to get a more controlled line, but this is not about control, is it?
This kind of experimentation is great fun. (And a super way to warm up and/or relax.) I'd love to hear other's ideas of makeshift, off-the-cuff funky ink applicator tools.