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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.
Are you asking for an application to design pcbs? If so, KiCad. You can start by playing around with boards on this list https://github.com/BenRoe/awesome-mechanical-keyboard/blob/master/docs/README.md
Figuring out the wiring for a handwire, or a starting point for a PCB, https://kbfirmware.com (don't use the firmware, outdated)
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.