What's the best open source app or utility that no one else has heard of?

(Please note that your replies may be read out and discussed on an episode of Late Night)

#VoiceOfTheMasses

@LateNightLinux SageMath! https://www.sagemath.org/ (or CoCalc, if you don't consider SageMath an app)
Although I imagine lots of people in academic circles have heard about it, it's probably not well known in the general open source community. My wife uses it for maths research in combinatorics, and I used to use it a bit in my physics education until I became a software engineer.
SageMath Mathematical Software System - Sage

SageMath is a free and open-source mathematical software system.

SageMath Mathematical Software System
@Qenupve @LateNightLinux yes! also, people knowing it are usually from particular geographical area :) Also, I believe that Sagemath creators did some frustrating math science assessing how broken is tend to be the math and code samples in scientific papers. Suggesting... Sagemath and it's Python interface as a solution.