is it possible to do the concurrent development? ...

Hi, Refer below links to know about concurrent development
forum.appian.com/.../Change_and_Configuration_Management
forum.appian.com/.../Change_and_Configuration_Management

Depends on the definition of concurrent development. Appian is a web based platform and multiple users can develop processes at the same time. Using sub-process architecture, your complex process can be split into multiple steps /milestones etc., which multiple developers can contribute in terms of development at the same time as well.