If you are looking for client management, then SugarCRM is great.

We use it to manage out client base. It is initially aimed at the sales process with lead generation -> conversions -> accounts, but yuou can use it for mail, meetings, documentation and there are a whole lot of addons.

There are two flavours, the Open Source version and a paid pro version.

SugarForge: Open Source CRM, CRM software, CRM Open Source, opensource CRM, SugarCRM

We use the Opens Source version and it does what we need, I am trying to find an integration to WHMCS to synchronise our clients

PM me if you want to talk more about it.