Sage CRM is a fairly powerful and flexible CRM application that I have been using in my current job since 2007. It's fairly robust, and allows for a lot of customization, and we have heavily customized our install of it. We have integrated it pretty deeply with our own in house order system, and our third party accounting software.

We are running it against an Oracle database. Sometimes I wish we weren't! Not that it doesn't run well on Oracle, it's that the company, Sage, does not seem to develop primarily for Oracle. Their main deployment platform is SQL Server, and the Oracle version seems to have some bugs that indicate to me that the developers are not Oracle savvy. Queries that could be written better, interesting and frustrating uses of Oracle sequences, issues with the query writing engine that sometimes breaks during patch upgrades, to name a few.

But, I can recommend the software itself, it is very good and extensible.

Tips and tricks of the Sage CRM software