A dead-simple markdown previewer in Vim thanks to KDE's document viewer Okular

okular-markdown-preview-vim.md

KDE's document viewer Okular renders markdown as HTML (and reloads it automatically on changes.) Thus, simply open the markdown file currently edited in Vim in Okular to be all set!

To start an GUI application from Vim, without freezing, hit-<enter> prompts or scrambling screen lines, one can add a command such as

if has('unix')
  command! -complete=shellcmd -nargs=1 -bang Silent execute ':silent !' . (<bang>0 ? 'nohup ' . <q-args> . '</dev/null >/dev/null 2>&1 &' : <q-args>) | execute ':redraw!'
elseif has('win32')
  command! -complete=shellcmd -nargs=1 -bang Silent execute ':silent !start ' . (<bang>0 ? '/b ' : '') . <q-args> | execute ':redraw!'
endif
command! OK Silent! okular %:S

to call okular by

:OK

With the most recent Vim, command! OK Launch okular %:S suffices.