A free program for Android, by cocoastudio.
One Jotter is a simple notebook with an extended keyboard that is designed for use with Markdown.
It is a free app, available for Android and iOS.
Themes:
There are a lot of beautiful themes available, all of them organized by color.
Change the font:
You can change the font and font size, and also use a variety of fonts.
Format the text:
It supports multiple formats, including HTML, Markdown, RTF, and plain text.
Preview:
You can preview the text in the Markdown format.
Search:
It supports searching both in the text and in the attachments.
Synchronize:
It supports synchronizing your notes with your Google Drive.
