The Crystal family was recently introduced by Alistair Cockburn 2. It is a set of AMs covering a broad range of needs in terms of the number of developers and project criticality, which may range from C (loss of comfort) to D (loss of discretionary money) and E (loss of essential money). Life-critical projects are not yet covered in these methodologies.
Crystal methodologies are described in terms of mandatory policy standards, which are very synthetic. Implementation details are left entirely to the discretion of the team. A specific methodology for Web development, targeted at 40 to 50 developers and with criticality E, is also presented (Crystal Orange Web).
Crystal methodologies are even less prescriptive than Scrum. They explicitly take into account the project size and criticality, and this could be a plus for project management. At the time of writing this chapter, however, they are less documented than XP and Scrum.