What is Crystal (agile) development method?

Crystal collects together self-adapting family of "shrink-to-fit," human-powered software development methodologies based on these understandings.

"Human-powered" means that the focus is on achieving project success through enhancing the work of the people involved (other methodologies might be process-centric, or architecture-centric, or tool-centric, but Crystal is people-centric).

Alistair Cockburn uses Crystal as a metaphor for a family of methodologies. The key idea behind Crystal is to tune the method to the type of project. There are two dimensions to a crystal — color and number. Darker color crystals symbolize larger projects with more people, which require “heavier” methods. Higher numbers in crystals symbolizes harder, higher risk projects, which require more rigor and ceremony.

In Cockburn’s words:

...the core Crystal philosophy is that software development is usefully viewed as a co-operative game of invention and communication, with a primary goal of delivering useful, working software and a secondary goal of setting up for the next game.

All Crystal methods begin with a core set of roles, work products, techniques, and notations, and this initial set is expanded as the team grows or the method hardens.

Team size: the Crystal Family accommodates any team size; however, Cockburn puts a premium on premium people.

Iteration length: Up to 4 months for large, highly critical projects.

Support for distributed teams: Crystal Methodologies have built in support for distributed teams.

System criticality: Crystal supports 4 basic criticalities: failure resulting in loss of comfort, discretionary money, essential money, and life.