I've been ending practices with this drill for many years. It works with either baseball or softball.
Split the team in half and form two lines at home plate, one staggered ahead and inside the other. The coach stands at the pitcher's circle with two bats. When he (she) hits the bats together, the lead runners in both lines take off. One runs straight through first base as if she is beating out a groundball, the other makes a turn and continues into second. You now have runners at first and second and two lines of runners still at home. At the next crack of the bat, the drill continues in the same manner but the runner on second now rounds third and scores while the runner on first takes third. Now every base should be occupied. It continues again, with the runner on third tagging up and scoring. Two runners will now score each time the bats are hit together. They will then return to the end of the opposite line and the bases will always remain loaded.
The coach can guage when the team has had enough and end the drill when the last player on line crosses home.
The drill allows for every baserunning situation, allows the coach to check running mechanics and proper turns and helps build stamina with short bursts. It's much more helpful than having the players continually circle the bases. You will find that the runner scoring from second will often chase the runner tagging from third home, making for a good game-type situation.