Are there any ad serving systems, that allow webmasters to serve ads from their clients on their sites? The client provides an image/text and a link and the website displays the ad in designated spaces. The website would display only ads from their own customers (nothing from a public ad network like adsense).
Can you please provide examples of such ad serving solutions? Preferrably free/opensource.
You can use an ad server like AdSpeed.com to manage, serve and track ads provided by your advertisers/clients.
You can try SmartyAds SSP for that purpose.