> real time preview of what you write

When I need that with a LaTeX document, I have vim with the TeX sources open on one half on the screen, and mupdf showing the compiled PDF on the other half, and a terminal in the background is running

  while inotifywait *.tex *.bib; do
    sleep 0.2
    pdflatex main && killall -HUP mupdf
  done

The sleep ensures that vim is finished writing the file before pdflatex runs. pdflatex is sometimes substituted for make or latexmk or whatever. SIGHUP makes mupdf reload the PDF. (If you're using e.g. Okular, it will pick up the changed PDF automatically, so that step can be skipped.)

(My intention is not to belittle cloud solutions, although maybe a little. :) Just to show how you can implement the real-time-preview feature with a very small shell script.)