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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.
I think it's a ratio of votes to time. I think as little as 4 votes can get something on the homepage if they come in fairly quickly.
The source code for hn is available if you want to go and look up the specifics. I'm not sure if this is the most up-to-date mirror, but the site doesn't change that often: https://github.com/wting/hackernews
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.