Based on the clinic of Rene Spandauw at the HBW Clinic on the 29th of December 1998.
This is a half court 5 on 5 drill.

The first team to make 50 passes is the winner of the drill. You do not have to score (yet). Losers run.
You are not allowed to dribble the basketball. A dribble or a turnover (travel, out of bounds) changes possession.
After you made a pass and before you can receive another one, you have to touch the baseline first. If you catch another pass before having touched the baseline, this is also considered a turnover and changes the possession of the basketball to the other team.
At the start and on any turnover you start over at mid court.

As said, the first team to 50 wins the drill.
After a while you can insert a few things to make it even more competitive.

First:
You can add scoring. You're still not allowed to dribble the basketball. But if you score a basket, you get 5 additional points. The team that gets the rebound will start again at mid court, even on a made shot.

Secondly:
If you score on a backdoor cut, you get rewarded 10 extra points. The team that gets the rebound will start again at mid court, even on a made shot.

Purpose of the drill
Passing
Catching
Pivoting
Moving without the basketball
Cuffing
Conditioning
Competitiveness
Finishing plays
Boxing out
Rebounding
Communicate
Teaching points
Meet the basketball ("shorten the pass")
Crisp passes
Pass away from the defender
Body balance
Catch, create space and face the basket
Protect the basketball (circle tight)
Hard cuts (will give you more outlets)
Talk; yell "ball" to receive it or say "no" when you think you're not open