A swimming board, also called a kickboard, is often used to improve the leg pedal technique when swimming. The best kickboards are of course the kickboards that give optimal buoyancy so that you can do the exercises undisturbed.
There are swimming boards with handles such as the Arena and ROKA swimming board. ROKA also has a variant without handles. However, this is ergonomically made so that you can 'hang on' comfortably