It’s easy to make a swerve drive, just build a pivoting wheel with a motor and you are done. Some issues around supplying power / control to the motor that is driving the wheel. To get around that you can build a Coaxial Swerve Drive. Both motors sit above the swerve wheel. Some form of gearing drives a shaft that goes down the pivot point to drive the wheel. A number of successful teams have Coaxial Swerve Drive, they are very nimble.
I came across this Lego swerve drive pic: LEGO Coaxial Swerve Module - CD-Media: Photos - Chief Delphi and thought it was pretty cool. I’m thinking of building one, but having a hard time with the upper support gear. I’m thinking of just drilling a hole in one of the large gears to pass the shaft through, but thought I’d throw it out here to see if anyone has any better ideas.