Is the "Free Order" discount working for anyone else in CartThrob 2.6 and EE 2.8.1? It seems to be completely broken - the cart still uses the undiscounted amount as the total. It looks like CT recalculates the total from scratch if it sees that the total is <= $0 in the total() function in cartthrob/core/Cartthrob_cart.php, but I can't figure out how to make it stop without breaking calculations for normal (non-discounted) orders.
I found a commented out line at the end of cartthrob/plugins/discount/Cartthrob_discount_free_order.php. I uncommented that line and commented out the replacement line (
return 0;). This seems to work, but I assume there was a reason it was commented out in the first place, so I'm not sure if I've broken anything else....