Primavera P6 and MS Project are both project management software, but they differ in key features. Primavera P6 allows for unlimited baselines and multiple users to work on a project simultaneously. It also features issue and risk tracking, as well as expense tracking. Primavera P6 is better suited for large, complex projects with many details, while MS Project is simpler and better for smaller, less complex projects. Reviews praise Primavera P6's control and flexibility for sophisticated, large-scale projects, but note the web client can be slow.