Open Contacts is an address book, or contact management program. However, it is not a CRM or PIM program.
If you find existing address book / PIM programs that your are using can not fit your needs, Open Contacts is a much more powerful candidate for you to consider. However, if you want event tracking, sale/marketing activities as well as billing etc., then Open Contacts is not for you. Obviously you should then eyes on CRM programs. Open Contacts is positioned as a bridge between conventional address book program and CRM program.
One of the features that make Open Contacts stood out of existing address book programs is its great extendibility to other programs running on desktop or the web. Though Open Contacts is not a PIM program, however, it is relatively easy to construct a PIM utility using existing programs. Please read
Build your own portable PIM with Open Contacts and other portable programs