Options like
bold or
italic in forums just need
javascript enabled, to show the buttons. That's all! In all browsers. And if someone hates javascript, it's still possible to type those styles manually, or use the forum macro.
As for spellcheckers, I don't know any forum that offers this, guess it's usually a browser add-on
In Firefox perhaps enabled by default, no idea, but in K-Meleon available too, just optional, if anyone wants it. Personally I hate those things, because in the job I'm forced to use MS-Office, and there it's extremely difficult to get rid of those ugly "word decorations"
But seeing that really many people need them, even I would opt to include that macro in KM by default too...