Meet VNote (https://tamlok.github.io/vnote/), a FLOSS multi-platform (Windows, MacOS and Linux; MIT licensed) note manager cum Markdown editor, with good documentation and some very interesting features -- namely its integration with Viki, an advanced wiki and webpage generation concept.
VNote is a Qt-based, free and open source note-taking application, focusing on Markdown. VNote is designed to provide comfortable edit experience, especially for programmers. VNote is NOT just a simple editor for Markdown. By providing notes management, VNote makes taking notes in Markdown simpler and more pleasant.
VNote latest 32 and 64-bit Windows portable releases (currently v2.7.2; untested!) can be downloaded from https://github.com/tamlok/vnote/releases.
Also, please heed the following excerpt from VNote's FAQ.
[Q.] How to make VNote more "portable"?
[A.] VNote will read and store configuration files in the common directory of the operating system to store application data. If you prefer to put these configuration files along with the VNote executable, you could copy or create the 'vnote.ini' file in the directory containing VNote executable. VNote will first try to read 'vnote.ini' from where the executable exists. However, please notice that VNote will store the notebook's path in the configuration file, so it may read a wrong path and complain about errors if you copy VNote to another computer.