Go to the mongrel web site and read their documentation on deployment options. You can use mongrel by itself, or with a front end web server like Apache. It also goes into some details on the advantages and disadvantages of each deployment option so you can make an informed decision on what best fits your needs.
I would recommend doing your research before posting your own speculations on what you feel are limitations in these technologies. Some very smart people have put these tools together, and they are very clear about what options you have. You just need to take to time to look into them.