Without the kart chassis, well there would be no racing. There are so many types of frames out there, as many small businesses make karts on their own to race locally.
A special note on the word chassis: Chassis is singular and plural. The singular version: (Chas-E). The plural version: (Chas-eez).
I know..interesting stuff; I'll get back to the real info:
The frame of a kart is made of steel tubing, typically an inch in diameter. They don't have a suspension so they need to be flexible so they can handle well in the turns.
As chassis get newer and more advanced they think of more ways to adjust the handling of the kart. The CRG Kart is an example of a karting chassis manufacturer that is continuously doing research and testing to create the most state of the art karts.
Some of these options are adjustable spindles(this is what holds the wheel to the frame), and stiffening bars you can attach or take off depending on how stiff you want the frame.
The steering consists of two tie rods connected to the spindle and steering column in the center.
All the chassis come with metal bumpers attached to them on all four sides.
An Open chassis doesn't have a roll cage. It's just the frame you sit on.
An offset chassis is designed to turn left. Phantom Karts are a big company in America for oval racing. It is faster on ovals. You can race on road courses but it's not recommended. (I did it once and finished 3rd out of 20, but I might of won with straight up!) As part of the offset of the kart, you are usually sitting left of center in the kart.
A straight chassis is designed evenly for left and right turns. Margay Karts are a good example of a straight chassis builder. The perfect type for a road course. You can also race this on an oval, but you are at a slight disadvantage. (I did this with a straight up Bandit Kart and did ok.)
A caged chassis has a roll cage. These are primarily offset and havier than the open karts. The chassis in these used to be very stiff until they started designing them as "floating chassis". They usually do this by attaching the roll cage to the bottom part of the frame and having springs/flexible rubbers between them so they can flex. They used to just weld it on, and it would be too stiff.
Beyond these types there are tons of different builds of kart chassis. The possibilities are endless but they are all kept within the rules of the division of racing they are building for. They are all pretty close in size and dimensions though, across all divisions.