Streight from the helpfile:

Returns the name of the Nth open dcc chat window.

Properties: ip, status, cd

$fserv(0) returns the total number of open fserves
$fserv(1) returns the nickname of the 1st fserve
$fserv(1).cd returns the current directory of the 1st fserve

If you specify a nick and N, it will return info on the Nth window for that nick.

/help $chat