The best alternatives to NUM are itch.io, Mathkeys by Parsegon, and Newton. If these 3 options don't work for you, we've listed a few more alternatives below.
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Postman Recorder by DevTools— Export Postman APIs from browser
itch.io is a simple way to find, download and distribute indie games online. Whether you're a developer looking to upload your game or just someone looking for something new to play itch.io has you covered.
Mathkeys lets you type in math on almost any website or program. Use it on Google Drive Apps, Piazza, Notes, iMessage, Messenger and more. No more copy and pasting the Unicode from Google - Mathkeys does it for you!