I found myself needing to texture two walls in a basement room and not wanting to get a sprayer to splatter drywall mud everywhere. What I came up with was a very fast, efficient way to achieve a similar effect without renting any equipment.
Assume that the walls are smooth to your satisfaction, i.e. you have taped and sanded the seams, filled in the screw holes, etc.
1 box of drywall mud
8 inch drywall knife
Step 1: Water down the Mud
I watered it down until it was about as runny as clam chowder. Just keep adding about a large handful in a bucket, then stir in water.
Rather than use a heavy mixer bit and drill, I just used a wire whisk from the kitchen.