FirstClass is a client–server groupware system. See the Wikipedia page.

FirstClass offers email, forums and file storage, nowadays also some more Internet features.
In the 90s, FirstClass was popular as a Macintosh BBS system, as it allowed connections via dial-in modems and offered a GUI for mail, forums and file exchange.
Connecting to the Internet via SMTP, POP3 and NNTP offered IP connectivity. It is also possible to connect FirstClass systems for data exchange between servers.
LAN connections to a FirstClass system could be made via AppleTalk, TCP/IP and IPX protocols.
The server is available for Mac, Windows and Linux systems.

On GlobalTalk, a FirstClass 5.5 system is hosted by @acn128@oldbytes.space in the zone BabCom.
This server offers an Internet eMail and Usenet newsgroups for GlobalTalk users.