What do you mean by IoT platforms?
The IoT platforms are suites of components those help to setup and manage the internet connected devices to remotely collect data, monitor and manage all internet connected devices from a single system. IoT platforms are the support software that connects everything in an IoT system. An IoT platform facilitates communication, data flow, device management, and the functionality of applications.
There are various open source IoT platform available in market which can be used for your IoT projects. Few of them are
Kaa IoT Platform
check out their key features here.
For cayenne vs blynk you can refer the article.
There are big industries who are the front runners in IoT platform and are for majorly for enterprise. find out about them.