I'm planning to do a basic comparison of some Area 51 statistics, so I've put the information of the first 15 sites in public beta into a small spreadsheet.
As asked in chat, I'll provide the data as a CSV dump in a community wiki answer here. Feel free to edit in more sites or updated statistics.
Disclaimer: I've tried my best to edit all the information exactly, but it's of course possible that I've made mistakes or typos (so there's no warranty assumed here). Additionally, all information is subject to rapid change.
Site,Days in beta,Questions per day,Answered,Avid users,Total users,Answer ratio,Visits/day
Bioinformatics,38,5.9,95%,49,957,2.1,281
Computer Sciene Educators,31,3.9,99%,51,"1,291",4.2,"1,177"
DevOps,115,3.1,84%,62,"2,248",1.9,386
Vegetarianism,143,0.1,98%,64,775,1.9,57
Korean Language,367,1,99%,65,971,1.8,299
Ukrainian Language,136,0.6,92%,66,"1,026",1.8,186
Artifical Intelligence,325,1.7,82%,70,"6,921",2,287
Arts and Crafts,423,0.9,95%,74,"2,162",1.9,844
Internet of Things,199,2.1,93%,83,"3,135",1.8,602
Language learning,444,0.8,91%,89,"2,448",1.9,77
Esperanto Language,304,0.4,100%,117,942,2.4,88
Literature,156,3.3,74%,126,"1,678",1.4,452
Monero,339,2.3,95%,172,"1,689",1.5,"2,432"
Sitecore,283,7.2,90%,174,"1,991",1.7,"2,042"
Retrocomputing,430,1.4,94%,189,"3,172",2.2,445