"Chiseling" Tool

It is getting to be Christmas time, and I have been waiting all year to design and print an ornament. I had a good idea for one, but I am having trouble finding the software I need to make it happen. My idea is basically a random 3d shape with flat side. Almost like a low poly sphere or cube or something. I don’t want it to look like anything specific. It would be as if I chiseled out random planes in a cube. Is there any software out there that could help me design this Christmas ornament? Some sort of online “chisel” software? Thanks!