Authentication API

Affects support for multiple languages or locales

The issue affects the manageability or productivity from the sysadmin perspective

Affects maintainability, code-quality, testability, quality-assurance, etc

Payment processing

Built-in data-import system

Built-in data-export system

Subsystem for identifying and merging duplicate contacts

Membership management components (CiviMember)

Built-in reporting components (CiviReport)

Composing, sending, and tracking email blasts

Event management components (CiviEvent)

Contribution management components (CiviContribute)

Case management components (CiviCase)

Activity management components