Netherlands
Former Opensource.com and Open Organization moderator/ambassador.
Robin Muilwijk
Former Opensource.com and Open Organization moderator/ambassador.
Aseem probably just wanted to use office applications as an example. But to give you an idea on other software that could be replaced by open source solutions, here are a few examples.
Depending on the features you use from Sharepoint, some of the open source and enterprise web content management systems could do the job too (Drupal, eZ Publish...).
Postgre SQL could replace SQL server or Oracle in a lot of cases. Windows server, well... if you are not running specific Windows software, the server versions from Ubuntu and other distro's can do that job too. Or get enterprise support by using RHEL from Red Hat.
A proprietary DMS could be replaced with Alfresco, an open source solution for an Enterprise Service Bus could be Mulesoft. Exchange can be replaced by Zimbra, or any other mail server of groupware like software (Zarafa is another groupware option).
As for small business like applications, they could look at OpenERP, and SugerCRM. Other software, like project management and reporting are also available. An example for project management: https://opensource.com/business/14/1/top-project-management-tools-2014.