Pitch into a blanket. You don't need a ballpark to practice softball pitching. Hang a heavy old blanket on a clothesline or between trees or poles, marking the strike zone with tape and stepping off the pitching distance used by your league.
Throw into a blanket. Just like pitching, you can practice softball throwing skills using a blanket as a catching net. Tape off a target, and practice throwing from various distances and angles.
Bat from a homemade batting tee. Not just for little kids, you can make a batting tee by putting a piece of rubber pipe over a thin post secured into the ground, making it the height of your strike zone. Place the softball on top of the pipe, and hit into the same blanket you use for practicing your pitching and throwing.