Fresh vegetables in August for my conditions are first and foremost green-shelled cowpeas. These come in many sizes and shapes and have different flavors, but they share one common trait: They love the heat and tolerate dry conditions. My favorite is the cream type, the foremost being the Big Boy, but I grow pinkeyes, one we simply call the Tommy pea, and blackeyes. For a change of pace, I like the Black Crowder and the Holstein.
I have grown lots of other varieties, but these are standbys. The little white peas like Lady and White Acre are delicious but more tedious to pick and shell.
Butterbeans are a bit more demanding, but they normally are reliable producers in August. I have settled on Mezcla as my pole lima of choice. It is a better producer than Carolina/Sieva or Willow Leaf. The big limas Calico/Christmas and King of the Garden do reasonably well, but I just don't favor the taste and texture. For the bush type, I prefer Cangreen/Thorogreen or Nemagreen. I grow Dixie Butterpeas as a change of pace. The big Fordhooks are not good producers here.
Okra needs water, but loves the heat. It will produce through September, but it really hits its stride in August. Emerald is head and shoulders above any other variety that I grow. I do grow some novelties like Buck's Big Buckhorn, which is decent but just not as productive.
There are a few other vegetables that produce in August. Eggplant does well, as do hot peppers, but cowpeas, butterbeans, and okra are my table mainstays.