There are 2 repositories under calculation-engine topic.
HyperFormula is an open-source headless spreadsheet for business web apps. It comes with over 400 formulas, CRUD operations, undo-redo, clipboard support, and sorting.
Jace.NET is a calculation engine for the .NET platform.
Agile Dashboarding, anywhere
Captain is a C program that calculates possible moves of ships.
a jace transform for transformalize
Resistance calculator for bringing a given input voltage down to one or more desired output voltages.