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BrogueCE
Brogue: Community Edition - a community-lead fork of the much-loved minimalist roguelike game
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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.
For a long time, most traditional roguelikes were free (although there seem to be more on steam lately). I think Brogue is a good place to start; it isn't too complicated, it has some nice quality of life stuff, cooperates with a mouse, and its pretty for its genre.
Loads of freeware Roguelikes out there too. See RogueBasin for a pretty exhaustive list. Dungeon Crawl Stone Soup is one I'd recommend.
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