Does Whalesync Replace Zapier & Make?

It depends, we use both for example. If you're using Zapier or Make for a 2-way sync, then we'd highly recommend you see if Whalesync supports that 2 tools that you're looking to integrate. Whalesync was built from the ground-up to be a 2-way sync integration tool, which brings with it many complexities, from how to handle conflicts when both apps are updated at the same time, amongst other things. An area that Zapier and Make lack immensely.

Can I Build Custom Automations With Whalesync?

No, Whalesync is not meant to be a custom automation tool like Zapier or Make, it is a data syncing tool, that allows you to sync data between tools in an incredibly powerful and seamless 2-way sync way.