Or alternatively an installable one for linux...
I mean a feature that propose on the fly alternatives while typing for the most common words, for instance typing "veh" would propose "vehicle".
I use ReText editor for Markdown text in Ubuntu, which I installed from Ubuntu Software. ReText is written in Python language and works on Linux and other POSIX-compatible platforms. The latest stable version of ReText can be downloaded from PyPI. You can also use the
pip install ReText command to install it from there.
Type in your markdown text and then press the Preview button to see what the formatted markdown text looks like. Alternatively you can enable live preview by default in ReText by selecting Edit -> Preferences -> check Use live preview by default.
ReText supports tabs, live text preview and syntax highlighting. Spell checking can be enabled with Edit -> Spell check -> Enable. Supported export formats: HTML, ODT, PDF.
All known third-party extensions for ReText are listed in Python-Markdown wiki.