How about Eric Lengyel's equation editor: https://radicalpie.com
There are also many suitable web versions such as https://editor.codecogs.com/
You can then download the image. The only thing I think they should add is the equation string as a comment to the images so you can upload and continue editing without a proprietary file format.
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There are also many suitable web versions such as https://editor.codecogs.com/
You can then download the image. The only thing I think they should add is the equation string as a comment to the images so you can upload and continue editing without a proprietary file format.