In Holacracy, all the actions that need to be taken care of in a company are called Accountabilities.
Roles are then assigned to people who have the skills and resources to fill them.
People can hold multiple Roles, even seemingly unrelated ones.
HR
iOS Development
Tech
e.g.
Office Management
Writing
Roles are flexible. Accountabilities can change...
Lead Programming
Prototyping
Hiring & Firing
… and new Roles can emerge out of shifting Accountabilities.  
Organizing Shifts
Blogging
Copywriting
Bug Testing
Click to Play
Newsletter
Roles can move between Circles
B2B Networking
Legal Communication
Roles
Customer Support
These Accountabilities are clustered into Roles.
Office IT
  and form Subcircles of their own.