I tested it briefly and confirmed that portably packaged MaNo left no traces in my system.
MaNo is the Markdown Notepad; it is a lean editor for the Markdown language, it generates HTML and provides performance tools [...] MaNo is GNU GPL V3 open-source software, code available at GitHub. You can download a 'light' portable version or a full installer (with syntax highlighting support).
Alas, while I really appreciate the Markdown features, MaNo is lacking too many basic features that I value in a text editor to be of much use to myself in its present form -- e.g., no case changing, no date insertion, no URL activation, and no automagic HTML preview.
According to its Github (https://github.com/mougino/MaNo), the portable MaNo doesn't include the code highlighter (https://github.com/andre-simon/highlight) of the installer version, although the later is also FLOSS.
MaNo latest portable release (currently v1.1.0, released 2017-04-27) can be downloaded from http://mougino.free.fr/freeware/#MaNo.