At the recent Consero 2010 Corporate Counsel Forum,a slide by a consulting firm arranged 17 software applications used by law departments. The arrangement presented a core group of four applications: matter management, document management, records management, and corporate secretary. Arrayed around them were nine more that primarily serve the internal legal staff: discovery management, intellectual property management, legal portals, risk assessment, collaboration tools, electronic billing, document assembly, and transcript management.
The outermost ring had four company-wide applications that find much use in legal departments but are not unusual to them: accounts payable, corporate intranet, Microsoft Office applications, and e-mail/calendaring. This three-level schema makes sense to me.