OpenACS 4 provides a skeleton on which to place web applications and
comes with several fine applications out of the box. (cms and e-commerce
being obvious ones). I expect to see more web applications produced for
OpenACS 4 after it's release. That puts it in a position to compete with the
other web application type platforms with the advantage that you don't get
nickel and dimed to death ($50 for file upload here, $300 for an e-commerce
module there) and that the modules are already designed to work together.