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couchers
The next-generation couch surfing platform. Free forever. Community‑led. Non‑profit. Modern. Chuck us a star :)
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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
you could also use couchers.org. It's more a follow-up to the broken couchsurfing.com, so a much wider scope. Currently it's free and says it will stay that way, they want to go with volunteer effort.
NOTE:
The number of mentions on this list indicates mentions on common posts plus user suggested alternatives.
Hence, a higher number means a more popular project.