WriteUp? That doesn't make any sense.
WriteUp is a sister web app to <htmleditr>, except this web app handles GitHub Flavored Markdown and regular Markdown. WriteUp even has its own mobile website that is compatible with mobile devices.
Features
- reads and writes .md and .markdown files
- copy the Markdown as HTML
- export your Markdown to HTML, PDF or a text file
- very customizable
- official Chrome App