Edited by author 07-31-2000 12:22 PM
I'm just posting this more detailed description, from the text of an old email, for reference:
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I propose a site that aggregates banner ads from hundreds of pre-vetted charitable organizations. A site builder can go there, see banners categorized by org type (with short descriptions and links to each non-profit site, naturally), select the ones she wants to show on her site, and finally arrange to have them auto-rotated by referring to a single .gif within her web pages. Further link tricks could allow tracking click-throughs.

Doing this would not only be a great thing in itself -- it would be great PR for the company that hosted it. If this company sold web-building tools, it could have tie-ins with site-building tools. Those who've gone "post-economic" via startups (others too) might be interested in working on it, in association with the hosting site. A list of credits down one side would be good.