Every aspect of the AssignCRM application can be accessed programmatically - whether retrieving a list of deals, getting a list of quotes or querying the calendar. You can also run actions programmatically - any button that you see in the application can be run through a JSON API request. It even has support for realtime updates, so you can connect systems together that will synchronize without any delay.
What's important is to know the different fields and types used in AssignCRM. The most important of these is the Deals type, which you can access through a simple URL such as /apiget.aspx?path=/Deals
Every request will need to be qualified with a username and password, base64-encoded. This is only the case if the user isn't already logged in to that session. This means the username and password will only need to be passed in once per session.
Next Topic: Customizing AssignCRM