Cyber Oz (sometimes stylized as "CyBER OZ") was an Internet Service Provider operating as part of the ESCOT (Entertainment Space & Comunication Technology) Corporation, a company that primarily focused on "bridging the real world and the virtual world".
The ISP operated from (roughly) 1995 to 2011 (based on when their website was last online).
The Cyber Oz City page would remain up for the complete duration of the company's operation, not going down until some time after July 4th, 2011. It is unclear if the Cyber Oz City servers were still maintained and/or kept online to this point, as the last news update on its webpage was the announcement of Version 1.4 on July 7th, 2001.
Testing this on a Windows 10 machine & a virtual Windows XP, while the initial installer that extracts most of the program's assets seems to function, the second "setup.exe" that contains the game's executable does not appear to launch at all.
To get around this problem and run Cyber Oz City, go into the "BIN" folder and create a shortcut to the "ANER533" executable. Right-click this shortcut and click on Properties. In the "Target:" text field, add the following:
Replace D:\Worlds\OzCity\ with whatever location you have installed Cyber Oz City to, then run this shortcut. The game should now function as normal.
Circa 2007, a page called "coc2.cyberoz.net" was added to the Cyber Oz website that would be home to another chat client known as "Hermit Crab Club" (sometimes referred to as "Oasis") - Judging by the mention of "coc2" in the webpage's address, this was a Flash-accelerated 2D successor of sorts to Cyber Oz City, though the Cyber Oz City page remained online alongside Hermit Crab Club for years.