Hello all!
I built a site that keeps track of the submissions on e621 and other furry art sites, and generates graphs and statistics every day. You can see it at https://furbitron.com .
Before I built it, I thought the most interesting thing would be the "all sites - all time" graph (for the big comparison), plus the "all sites but FA - all time" graph (so the smaller sites aren't "lost" at the bottom of the all-sites graph). Now I think the year-on-year graphs for the various sites might be the most interesting.
I know that https://e621.net/stats exists, and Furbitron cannot easily replace it. Most other sites don't provide much in the way of stats, though, so Furbitron can be helpful to make comparisons between sites.
The "live" data for e621 comes from the API once a day, using a program that (as far as I can tell) complies with the API requirements. The historical data came from a one-time download of the database dump that e621 provides.
For other sites, the "live" data comes from that site's API (if available) or by grabbing the "new submissions" page and parsing the HTML (if no API), once a day. The historical data came from asking the site for either a series of submission numbers or dates, depending on the site's capabilities.
Thanks!
Furbitron
https://furbitron.com