The Markdown plugin integrates peg-markdown easily as a loadable plugin. The original library can be found at https://github.com/jgm/peg-markdown.
The TextCaptcha plugin can be installed using the usual Ambition plugin tool. The plugin will link with your application.
The Markdown module will parse Markdown content in a string, and return a string containing HTML.
In a model or controller:
using Ambition.Helper;
public void example_method() {
string result = Markdown.process("# Header\n\nContent!");
}