This is another One Markdown feature to create equation. 
This type equation is an image display in OneNote, it is not the OneNote native equation.

One Markdown 2.0 add create flow chart feature.

You can use markdown to create flow chart for OneNote

"Gem for OneNote" v39.4 add a new feature to help you copy MathML out from OneNote equation.

One Markdown add new Markdown Syntax to help create Heading Anchors, it can jump inside a page just like jump inside a web page.

Gem for OneNote has provided Create Table of Contents of Headings for OneNote by One Click.

This article is show another way to create table of contents of headings for OneNote. It use Markdown in "One Markdown" to create table of contents for OneNote.

One Markdown 2.0 add highlight syntax for code block.

You just need to add programming language name after begin tag ```.

One Markdown 2.0 add new Markdown syntax to insert check box.

You can install One Markdown for Android in Android phone, using [ ] and [x] to insert uncheck and checked To Do tags for OneNote.

One Markdown 2.0 add convert MathML XML to OneNote equation feature.
You just write MathML XML in One Markdown, "One Markdown" connect to "One Markdown Server" to convert MathML XML to Equation and save into OneNote.

MathML XML -> One Markdown -> One Markdown Server -> OneNote

Security Setting - Unknown sources

​Allow installation of apps from unknown sources.

Settings -> Security -> Enable "Unknown sources".