For several years, marketplaces exist in the software industry, where customers can, for instance, search for specific services offered by different vendors, review, buy and use these services. The vendor-sided characteristics of these marketplaces are widely discussed but have not yet been investigated in detail. In this paper, we consider online marketplaces and the participants as part of a Software Ecosystem. First, we derive vendor-sided characteristics of a Software Ecosystem from existing literature and introduce FaDOM - a newly developed software Framework for Automated Data Collection in Online Marketplaces. On basis of the collected data, we analyze vendor-sided characteristics of five online marketplaces.