kramdown 是一个用Ruby实现的Markdown的解析器。Markdown是一种轻量型标记语言， 其目的在于为以网页为载体的文章的排版提供一种较HTML来说更简便、更安全、可读性更强的书写方式。它并不是HTML的替代品，使用Markdown的 语法编写的文章最终都要通过其翻译器转换成HTML代码。
kramdown (sic, not Kramdown or KramDown, just kramdown) is a free GPL-licensed Ruby library for parsing and converting a superset of Markdown. It is completely written in Ruby, supports standard Markdown (with some minor modifications) and various extensions that have been made popular by the PHP Markdown Extra package and Maruku.
It is probably the fastest pure-Ruby Markdown converter available (February 2012), being about 4x faster than Maruku and about 5x faster than BlueFeather.
If you want to get started with kramdown, have a look at the installation page to see how you can install it on your system. Then look through the documentation for finding information about how to actually use kramdown and its parsers/converters. The quick reference provides a overview of the syntax – if you need a more detailed description of the superset of Markdown which kramdown supports the syntax page is the place to go.