Vtiger is an open-source CRM suite, originally forked from SugarCRM due to the commercial activities of the SugarCRM team. Vtiger aims to be open-source, although it does have the possibility of purchasable extensions, much like Joomla. There is a lot of history in the fork, much of it best left alone. The main point to remember is that SugarCRM and Vtiger are released under different licences. You need to check that the functionality you require is available under the licence you wish to use.
From what I've used of it over the last few years, vtiger is well ahead of many of the smaller commercial CRM applications, but lacks in the breadth of functionality found in the heavy hitters, such as Oracle/Siebel and similar offerings. However it's free, it has an active help forum and it looks good. I've been using it when consulting to break a client's perspective of what they want out of CRM. Just playing around with Vtiger for 10 minutes helps them think and articulate what's good and bad about their current system and Vtiger.
I've always found CRM systems to heavily biased towards sales or service. This lies in the origins of the applications and was more more obvious in the earlier days of CRM. For instance, Siebel was heavily biased towards sales and hence had a wealth of sales and marketing functionality whereas Clarify was biased towards service, having a wealth of service and support functionality. Now that the CRM field has had time to mature, increase functionality organically and increase more aggressively through acquisitions, CRM suites present wider functionality than just sales or service. This has been increased further by the need to integrate to ERP (Enterprise Resource Planning) suites. In many cases, that's lead to acquisition, e.g. Oracle's acquisition of Siebel.
vtiger CRM is more sales biased with a lot of the functionality surrounding Leads, Campaign Management, Prospects and conversions to Sales Accounts. There is also a lot of reporting functionality and a number of modules surrounding a service-centred approach, e.g. product inventory, FAQs, trouble-tickets and a customer portal. Not bad for open-source.
A typical tenet of CRM is to be able to see all of a customer's activities at a single glance. vtiger goes someway to providing this in that the Contacts screen displays a lot of the entries on the related entities, e.g. Trouble Tickets, Quotes, Products, etc. What it doesn't show is a list of interactions between your organisation and the contact. Think of a typical call-logger or call-tracker. In many applications, it would be the contact history (where the term contact is being used for the interactions, rather than a person). That to me, is a fundamental gap in vtiger's functionality. However, from what I can see, it may not be too difficult to customise vtiger to allow this. It may even be possible to do this through the configuration screens without writing any code, e.g. cloning a trouble ticket module and entity, changing the new entity's types to be more relevant, etc.
vtiger is open-source and hence, free to install and use assuming you have the necessary hardware and software to install it on. In addition, there appear to be three methods that commercial organisations are generating revenue through Vtiger CRM.
The bounty scheme crosses the line between 2 and 3.
If you know enough about installing and configuring CRM systems, also have sufficient knowledge of MySQL and php, you may not need to pay anyone anything. That's where I'm headed.