Hopefully, it's possible to play "Connect5" at BK using the interface of Connect6. Of course, it is proper to do it in "Unrated game", "Not counted game" mode. If you want to test "Connect5" write here.
The rules of "Connect5" are in my post below from 15. May 2007, 21:14:11
Illegal move (two pieces at the same line) means the immediate lose.