Tarps work great for both hammock-ing and ground camping. The 10x10 tarps at Bushcraft Outfitters are my favorite. They have reinforced webbing tie-outs instead of grommets.

Here's my BCO 10x10 configured for ground camping.
There's a BCO 5x7 inside as a ground cloth.
image.jpg

(Ugh. My pic is upside down. Oh well)