eXtreme Programming - XP was created by Kent Beck, who compiled a collection of good practices and took them to the extreme. Its mostly targeted at small to medium sized projects and has gained rapid acceptance and practice over the world.
The five XP values are communication, simplicity, feedback, courage, and respect. Its hallmark principles are planning game, small releases, metaphors, simple design, refactoring, pair programming, testing, collective ownership, 40-hour work week, on-site customer, coding standards, and continuous integration.
Customers provide the specification of required functionalities in the form of user stories. They are written concisely in non-technical formats and focus on the needs of the user avoiding any design details. They help the developers to estimate the implementation time and go into the release planning.
Each short iteration achieves a handful of tasks and its recommended that a steady project velocity be maintained. Developers work in pairs and perform unit tests and integrate code often. The customer is ideally available on-site and is closely involved in the development through rapid feedback. Refactoring the code to renew obsolete designs and remove redundancy allows for a higher quality product to be produced. Testing is an important part and is undertaken frequently in form of unit tests and acceptance test. Finally lengthy documentation is avoided and optimization is left till last.