Discord renders whatever Unicode text you send exactly as typed, but it has no built-in font picker, so every 'Discord font' you've seen is actually a different block of Unicode look-alike letters standing in for the alphabet. This tool generates all the popular variants at once (bold, italic, gothic/fraktur, double-struck, monospace, and more) so you can compare them side by side and copy whichever fits your server's vibe straight into a nickname, status, or message. Because they're genuine Unicode code points rather than an installed font, they'll show up the same way for everyone in the server regardless of their device, the only caveat is that a few very old or accessibility-focused clients may render rarer blocks (like double-struck) as blank boxes.
Chat apps render text using the reader's own system font, not a font chosen by the sender, so there's no per-message font picker, Unicode look-alike characters are the only way to make your text visually distinct for everyone.
Bold, Italic, and Sans Bold tend to render cleanly across nearly all devices and fonts, while less common styles like Double-Struck or Monospace occasionally show as boxes on older phones.
Underline and strikethrough are combining marks layered on top of any base text, so you can run your text through one of the letter styles first and then apply underline separately for a combined look.