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LibreOffice
Read-only LibreOffice core repo - no pull request (use gerrit instead https://gerrit.libreoffice.org/) - don't download zip, use https://dev-www.libreoffice.org/bundles/ instead (by LibreOffice)
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FreeCAD
This is the official source code of FreeCAD, a free and opensource multiplatform 3D parametric modeler.
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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.
Otherwise, maybe a basic drawing program... the Draw package in Libre Office is an option
Depends a lot on your budget and software background... Myself, I'd recommend a CAD program. Either a freebie like FreeCAD or one of the paid options. (I personally use the Maker version of SOLIDWORKS ($100/yr), because I'm familiar with it from work.)