Which brokers can work with cTrader?

Question

Electronic commerce

Immediately - I do not understand the topic well.
Brokers have the opportunity to open different types of accounts and they have a point of support for certain platforms: ctrader, metatrader, etc. But it is not clear why one type of account has cTrader support, while the other does not (metatrader comes by default)?
I want to decide if a broker is right for me before registering and opening an account.