Qalculate! - Qalculate! is a multiplatform multi-purpose desktop calculator.
Eve - Programming designed for humans
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.
Jupyter - Project Jupyter exists to develop open-source software, open-standards, and services for interactive computing across dozens of programming languages. Ready to get started? Try it in your browser Install the Notebook.
PyCharm Community Edition - "The intelligent Python IDE with unique code assistance and analysis, for productive Python development on all levels."
Calculist - The open-source, web-based thinking tool that facilitates effective thinking for solving problems.