This Keep Notes app support Markdown, you can write, preview, and publish your notes in Markdown format. It also supports finding notes quickly with instant searching and tags. You can share or publish your notes online.
When you modified your notes, the notes are backed up. You just need to drag the version slider to go back in time, which is a very useful feature.
Simplenote uses Simperium to store and sync notes across multiple app platforms. The Simperium libraries handle all the networking so developers can focus on building a great user experience.
What’s the most important, it’s all completely free software, you can free download the Keep Notes app and use it.
SimpleNote supports platforms: