One of the reasons to use CRM is so that everyone has access to customer information in order to better serve your customers. One database of knowledge about every client is an asset to your business and for service.
If you want to sell your business, you will need a customer management system in place to pull sales and contract information for potential buyers, investors or even in some cases banks.
Here are 3 open source CRM tools: opebCRX, CiviCRM, and Zurmo. Zoho currently offers a limited free version for up to 3 users. Of course, if you are Microsoft shop, you have access to Dynamics, but in many cases that will be overkill.