At the end of each quarter, I visit Family Tree DNA's (FTDNA) Projects page and copy into a spreadsheet all the names of the surname projects along with the number of participants. I then sort them in order from the largest to the smallest. A listing, in decsending order, of the projects with 50 or more participants can be found by clicking on the "List of Projects" link above. The other testing companies don't supply participant numbers, but a few administrators have supplied me with their figures, and they are included in this listing. If anyone with projects using the other companies, or multiple companies, would like to be placed on the list next time, please contact me.
On the Summary page, is a chart which shows the totals from FTDNA projects and how they have grown since the previous quarter. Those who use other companies and have notified me, are listed in the "50 plus" list but not in the summary charts. Since individuals are allowed to participate in more than one project, there may be some duplication. However, I suspect most second projects are geographical. There are also several projects in this total that are technically not a surname project. However, they are listed at FTDNA as a surname project, so I don't try to make any determinations.