Here is a video I am sharing, its about a robot which is commercially available. This robot is not using any wheel or anything, just using its angular movement to actually move like real snake.

The new ACM-R5H swimming in a new pool. It is fully customizable in its colors (fins and body) and in the electronics that may be fitted in the front and rear unit. The robot length can be also easily changed by adding or removing units, in this case it is a version of 6 active joints.