What are pendulums used for today?
They are used for both traditional and modern purposes
Apart from many old-style uses (like clocks or hypnosis, for instance) they are used in many other ways.
Some skyscrapers are built with a huge pendulum inside its upper floors, so that it takes the most of momentum due to the wind. This way, the building structure remains steady.
There are many other purposes which pendulums are used for; a quick search on Google or DuckDuckGo could give a lot of information.
Pendulums' utility is based on conservation of momentum and periodicity of oscillations.
P.S. I do not have too much time to answer this question, sorry.