This is the technology that I feature, and I recommend it highly to organizations that are serious about quality. The key Cleanroom techniques are specific, interrelated ways of doing semiformal specification and verification, testing, and incremental development.
Testing serves primarily to measure quality, and only secondarily to detect residual defects.
Progress during development is visible and measurable. Integration is relatively painless. Debugging and rework consume a minimal fraction of the total effort. Since 1993 I have been teaching this technology in a university course and in an intensive short course in industry. Here is a paper describing Cleanroom, the course as taught at New Mexico Tech, and some of the results that we get using the techniques taught in the course.