This webpage analyzes the degree of decentralization in two distributed social network ecosystems: the Fediverse (including Mastodon, Pixelfed, etc.) and Atmosphere (including Bluesky, WhiteWind, etc.). It uses the Herfindahl–Hirschman Index (HHI), an economic metric to measure market concentration, which is calculated as the sum of squares of market shares of all servers or nodes. HHI values range from near zero, indicating a highly competitive, decentralized system with many evenly distributed servers, up to 10,000, indicating high concentration or monopoly, where most users are on a single server. Economically, below 100 is highly competitive, below 1500 is unconcentrated, and above 2500 is highly concentrated. The site focuses specifically on active users' data distribution: in the Fediverse, data is held on servers/instances, and in Atmosphere, on Personal Data Servers (PDSes) that host user data repositories. It provides current statistics on the number of servers, the size of the largest server, and the remainder share for both ecosystems, along with visual gauges (though exact figures are not included here). Source code and data are available on GitHub for transparency and further exploration, encouraging contributions for additional metrics or analyses of resilience and distribution. The page is maintained by Rob Ricci, who provides contact links on decentralized platforms. Overall, this resource offers an ongoing quantitative perspective on how decentralized or concentrated these emerging social network ecosystems currently are, aiming to inform and invite community participation.