You can fill it to begin with using affiliate links to existing web apps. Once you get a decent number of people using it, you can allow people with new web apps to advertise there, or charge for subscriptions to be listed there, or take a cut out of every sale/signup. Many ways to skin this cat.
Also provide extensive curation and guidance. Whether through analytic indexes, "best of" pages for different categories, or a questionnaire for visitors to fill out and get a personalized set of recommendations.
You can fill it to begin with using affiliate links to existing web apps. Once you get a decent number of people using it, you can allow people with new web apps to advertise there, or charge for subscriptions to be listed there, or take a cut out of every sale/signup. Many ways to skin this cat.