The example that comes to mind (probably for most people) is Hinduism. All you need to do is go to India and you will see that the Indian worldview is completely polytheistic. This basically means that the Hindus believe that there are many gods and goddesses. Moreover, Hindus worship many of them simultaneously.
You can see this in various contexts. For one thing, if you just walk around the city, you will see many temples and even idols. Also if you ever try to share about your belief in God, then they may even adopt your belief as well. There is no notion that just because they believe in your God that they must give up their gods.
This framework shows the worship of many gods at the same time.