No other uses I can think of. You use an umbrella in it as it was intended for. I had a recent job which it was handy because I didn't have room for a softbox or the time for a more elaborate setup.
Adapt one of these https://www.bhphotovideo.com/c/product/31902-REG/Lowel_T1_50_Flexi_Shaft_Pack_of.html and then put a small flag in front of the light https://www.bhphotovideo.com/c/product/32264-REG/Lowel_T1_52_Tota_Flag_8_x.html is one possibility that I've used. You could stick a gel holder in there for color/ND gels. You could stick all manor of shapes to cast shadows on a rod. But some of this depends on the type of light, most of this is pointless on a big bare bulb type of fixture (like a Rifa), so the light type is a bit of a required piece. And yes I know, a Rifa like light is not going to have an umbrella mount, it's just an example of something that doesn't work with the suggestions above.