What are the best marketing tools for Web-Applications?

Hi!

How would you in general market web-application? They typically don’t have much content and besides the landing page, most pages are generated dynamically depending on the user and are therefore not public. So basically this is not the best starting point to get many users over search engines. Additionally, to use the site, a user has to do something actively (login, fill out a form…) which is an additional “obstacle” to get a user base. Since there are these differences of web-apps compared to blogs or other mainly content related sites, do you think also the marketing for such sites should be different?

Thank you!