It was accessable via modem at 2400bps. I (DouglasBagnall) only ever used a dos based VT100 emulator, but I believe by the end you could use SLIP or PPP, should you be so inclined. You could dial in as often as you liked but would be cut off after 3 hours. In the evenings it could take hours of dialing to get through.
The system used VMS of some form. In 1991 or 1992 I saw it being used for IRC and email; presumably telnet, news, and ftp were also available. By early 1994 Gopher was added, and in March that year an internet magazine (@punnet) was published in Wellington, based on articles dragged from gopherspace onto a Citynet-connected Mac SE.
In the early days the mail program was horrific. Its editor was of the type that really would put ^H^H^H^H in your message when you wanted stuff gone, and to make things worse, I never found a cancel button. OTOH, you could blame typos on line noise. Sometime in 1994, they put Lynx and Pine? on the box, which bought it to such a state of perfection that the only thing left to do was to close it down.