Qalculate! - Qalculate! is a multiplatform multi-purpose desktop calculator.
SpeQ Mathematics - SpeQ is a small, extensive mathematics program with a simple, intuitive interface.
GetBricksApp - Bricks is a note-taking web app with a built-in calculator. It can be installed as a desktop or mobile app, because of PWA technology this app built with. Which is also makes it offline available. Notes created with Bricks can be shared.
PyCharm Community Edition - "The intelligent Python IDE with unique code assistance and analysis, for productive Python development on all levels."
NumWorks - The graphing calculator that makes learning math easier.
Microsoft Office Excel - Microsoft Office Excel is a commercial spreadsheet application.