Skype formatting

This seems to be nowhere documented, but here's some markup Skype recognizes.  An example of what you'd type is in gray, and what Skype would render is in blue.

*bold*
bold

_italic_
italic

~strikethrough~
strikethrough

@@ *not bold* (note the space after the two at signs, and that this must be the first thing in a message)
*not bold*

!! preformatted (note the space after the two exclamation points, and that this must be the first thing in a message)
preformatted

Preformatting also overrides other markup, for example
!! *not bold*
*not bold*

Preformatting also respects whitespaces, for example
!! above
below
above
below

Of course Skype also supports /me, like most chat clients do these days
/me yawns
[user name] yawns
[user name], will be whatever your name is in Skype (not your username)

And since 6.22.81.105, you can also enable/disable the markup feature with
/wikimarkup on/off