In my group we have adopted Scrum, along with a "Heat" variant. That is, a Heat is 3 month-long scrums. During the heat we are expected to release something for our stakeholders to preview (Sprint 1), collect feedback while continuing development (Sprint 2), and integrate customer feedback as appropriate and release (Sprint 3).

Here are the basic rules:

• A Heat is three (3) Sprints.
• A Sprint is one (1) calendar month.
• One (1) week planning iterations are used for engineering purposes.
• The goal of a month long sprint is complete code ready for release (the features implemented are complete).
• The goal of a planning iteration is to keep planning to a short time period enabling more accurate estimates by developers.
• The stories for the month long sprint should be well defined prior to the inception of the sprint, t-shirt sized to gauge the anticipated story load for the sprint, and prioritized.
• The sprint backlog defines the release for the end of the sprint.