Zoho has more than 50+ apps which need integration with each other and with third party apps like twitter,google, Salesforce etc.Using Connection and Invoke URL, Integration can be done between Zoho Service and other third party apps.
By default Zoho provides built in integration with many app such as Gsuit,Office 365,Slack,Shopify,Facebook ads and many other such apps for these bult in integration you just need to enable or disable these integration
Other then this Zoho has a market place where Zoho Partner develop and upload their free/Paid extensions/custom apps which provide custom integration with third party services. Using these extension/custom apps you can extend the functionality of your CRM.
If an app/extension and Zoho built-in integration does not full fill your business requirement then Zoho developer comes into picture who knows in-out of Zoho Integration method Connection and Invoke URL.