I had no idea what an open-source CRM was, either.
Put simply, it means the source code is open for viewing and editing. By nature, it allows for greater customization and flexibility - you can see only the data you want to analyze, for example. For broker/owners, adding new agents won't cost you a dime. And because you're not locked into a contract, changing products is a cinch.
Best of all? Unlike proprietary software, open-source software (OSS) is typically low-cost or free.
If you've been keeping track of relationships with clients and leads with spreadsheets due to concerns over cost, consider adopting one of these open-source CRMs with free installations:
SugarCRM Community Edition
The preceding was adapted from RISMedia.com.