Android

Termux Monet - Termux-Monet is a unofficial, modified fork of Termux, an Android terminal application and Linux environment, with Monet Theming Implementations. ⭐

Monet means Material You theme!!
Mathematics (Android app name) - Calculator with many cool stuff related to math like graph and it calculates algreba, function, formula, etc. ⭐
anemo | Fdroid - A open-source Local private storage for Android

Anemo is a private local storage utility application for android. Instead of being a stand-alone file manager user interface, it hooks into various components of Android making it feel like a native part of the operative system. Moreover it provides ways for the user to export contents from other apps and save them as files.
Gesture Suite - one gesture app to rule them all

Window

United Sets - It allow you to group other softwares together in browser-like window and each software represent as tab, helpful for multi-tasking.
Shell | Report/track issues on issue repo(NO open source ig ) - Powerful manager for Windows File Explorer context menu(right click menu)(many features added in context menu).
Flow Launcher - 🔍 A Quick file search & app launcher for Windows with community-made plugins