It's open source and you can get the source code form https://github.com/yguan/notepad. You can also try it out on the web before installing it (http://yguan.github.io/repos/flexnote/#/notes).
If you prefer a in-browser version, you can get it from https://chrome.google.com/webstore/detail/flex-note/ckhmolgiclhlbmndaffmhddfdgbokbhb.
Warning:
If you use "Clear browsing data", please make sure the "Hosted app data" checkbox is unchecked. Otherwise, the app data may be erased.
Known issues:
1. Newly added note doesn't have focus on the editable field
Upcoming features:
1. Set the background color of a note
2. Import and Export of notes