The Zoho CRM Contextual Gadget for Google Apps will be visible only if your Google Domain's Super Administrator enables the service.
To enable the service:

1. Go to www.google.com/apps, sign in with your domain name and go to the Admin Console.
2. Log in to the Google Apps domain with the super administrator's privileges.
3. In the Admin console page, click Apps > Marketplace Apps > Zoho CRM.
4. In the Settings for Zoho CRM page, click the More icon > ON for everyone.
5. Click Turn ON for Everyone if you want all organizations to view the contextual Gadget. If you want only some organizations to view it, select ON for Some Organizations.

The service will be enabled within 24 hours and you'll be able to view the app in future.