Weather, Climate, and Natural Hazards NOAAport - provided by US NWS but has international data, forecasts, and messages also
Open Source Reception and Data Passing Software LDM, Unidata's Local Data Manager Main site
GitHub Repo
Open source sharing network [iNOAAport](Cooperative network of servers for sharing over the Internet)
NBSP software
OpenNOAAport, UPR's servers
International Civil Aviation Organization Seismo, Earthquakes, Volcanoes, Tsunamis
A number of these are passed via Weather comms channels mentioned previously
Volunteer / Citizen-provided information APRS - Amateur Packet Radio Service
Location tracking for storm spotters
Automated stations can report weather, environmental, and other information
CoCoRaHS - Community Collaborative Rain, Hail and Snow Network Main site
Blitzortung - a worldwide collaborative lightning detection network Main site
DNS Blocklists and other Internet community security efforts
github/caesar/awesome-public-datasets
Edward Tufte - data visualization books (the "Bible" of data viz books)
subreddit "Data is Beautiful"