As someone said already, Markdown was designed to be compiled to HTML, and browsers are the best HTML renderers we have. While you can technically interpret it semantically and render it without a browser, you would still need to support HTML since Markdown supports embedded HTML (e.g. `<details>` tag is a popular one to hide information). At that point you probably are better off using a browser anyway.

By the way, while browsers can be both CPU and memory hogs, they're not inherently inneficient and it mostly depends on what the website is doing. This project uses minimal JavaScript and no frameworks, and while I didn't measure it I assume this site should be reasonably efficient, both in memory and CPU usage.