Abacus is a calculator with a small math language that supports user-defined variables and functions. Try it out!
Abacus uses Haskell with Reflex. I recommend building Abacus with GHCJS. Here's how, assuming you have GHCJS installed:
npm install
cabal v2-build --ghcjs
This should create the folder dist-newstyle/build/*/*/*/build/abacus/abacus.jsexe, where the *'s depend on your system.
Open index.html in that folder in a web browser.
If you use Visual Studio Code, this repository uses a dev container that comes with GHCJS.