This document introduces and compares three software development methodologies (SDM): Waterfall, Agile, and Rational Unified Process (RUP). It analyzes the strengths and weaknesses of each, outlines which types of projects and industries each is suited for, and recommends adopting RUP for implementing a new platform. Key points covered include iterative development approaches becoming more prevalent, the benefits of RUP including iterative testing and adapting to changing requirements, and its suitability for medium-large teams and critical systems.