Mastodon
distributed, interconnected microblogging
forem
the platform that powers dev.to
Diaspora
community-run, distributed social-network
lobsters
link-aggregation site, inspired by Hacker News
Feedbin
open-source feed reader for multiple platforms
Danbooru
taggable image board
Catarse
open-source crowdfunding platform
OneBody
church management software
if-me.org
mental health communication
Juvia
commenting server of the likes of Discus or IntenseDebate
Organization for Transformative Works Archive
archives of fanworks, including fanfic, fanart, and fan vids
PublicLab.org
collaborative knowledge-exchange platform
OpenFoodNetwork
software to manage the lifecycle of food
Open-Source Event Manager
event management tool tailored to conferences
Annict.com
anime website
iNaturalist.org
social network for nature stuff
Calagator
community calendar platform
Hackershare
social bookmarking and knowledge-sharing
LearnAwesome.org
social network of learners
Human Essentials
management system for essentials banks
Covidlist
connect vaccinations with those who need to be vaccinated
Terrastories
geostorytelling
Bike Index
the internet's bike registry
World Cube Association
everything for the World Cube Association
icare
carpooling platform
vglist.co
video game library tracking
Splits.io
speedrunning data and analysis
ebwiki.org
database of police abuse cases against people of color
Skyderby
flight analysis and competition scoring
visualizer.coffee
visualize hipster coffee machines
Racing On Rails
bike racing association management
Open Split Time
endurance event data management