Plain text with just enough punctuation to imply formatting, which is why it ended up as the default for READMEs, issues, wikis and notes. Its tables are the awkward part - a pipe-and-dash grid that's readable enough written by hand and tedious to maintain by hand.

Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop a Markdown file above and choose afterwards.