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.