I use a couple of tools:

1. Hackmd.io
   Is a markdown editor that supports HTML. It shows coloring for code like python. It requires basic HTML knowledge.
2. QuickTextPaste
   Is a freeware tool that allows me to input prewritten HTML commands with quick access buttons.
3. ezgif.com and giphy.com
   Both platforms where I can convert videos into .gif edit them only and even combine them.
4. Markdown to HTML online converters
   Just as it says.
5. LaTex image editor
   For modifiable images that hold mathematical equations.

I'll make a detailed post about this in the close future.