Retro PC Gaming

TeamSpeak was written out of frustration with currently available similar
products. Being two hardcore team game players, the creators (wow that's us)
of TeamSpeak could not find a (freeware) program that suited all their
needs. The demands we had seemed simple. We wanted reasonable voice quality
(so you can actually understand each other), low bandwidth usage (for the
poor people with isdn) and no connection troubles (if you can play a game on
internet, you must be able to use TeamSpeak).
Surprisingly, we found no such program. Most popular are RogerWilco and
Battlecom.

RogerWilco has an awful sound quality and uses tcp to send voice data. This
is a bad idea and fills up low bandwidth connections really fast.
Battlecom has a nice voice quality, but has an awful network protocol. Odds
are, that if you share your Internet connection (ICS, MASQUERADE) you can't
use battlecom.

So we created TeamSpeak. It uses only 640 bytes per second upstream MAXIMUM.
It has a reasonable voice quality and it can almost always connect. If you
can play a game on internet, you can use TeamSpeak. Also we have some great
ideas for future versions and we are planning a linux server version.
Because we are nice guys and want to make the gaming community more
interesting, we decided to make TeamSpeak freeware. This means that you can
download it and use it for free. Also we did not include any annoying
banners or shit like that. Totally free, totally no shit.
So enjoy this little program and improve your teamplay with it.

So far and as far I can tell, there's no official system requirements. The only official system requirement is having the protocol TCP/IP installed in the client machine, since TeamSpeak Classic uses TCP/UDP ports to connect to the server, no matter if it's in the same machine or a different one. For Clients, you can connect to the server without port fowarding, just for the server this is a requirement.

TeamSpeak Classic as the quote suggests from the original devs, It was the first VOIP Freeware software for 'gamers'. Roger Wilco actually is the first VOIP for gamers, but it required a subscription in order to access the servers and it also needed constantly Internet after accessing the servers which back in 1999 it was a thing for few people. TeamSpeak Classic was made thinking as an alternative to RogerWilco (Back in the year 2001 it was bought by Gamespy and few years later Microsoft bought the program and implemented as part of the Xbox infrastructure).

So you can say TeamSpeak Classic was the real VOIP for gamers, totally freeware, voice quality wasn't great, but it was possible back in the year 2001 to understand each other at least. 

TeamSpeak Classic is really not recommended to use, unless if you have a very old machine such as Windows 95/98 or a very weak machine, otherwise if you have about 1GB of RAM, It's recommeded keep up with TeamSpeak 2, since it has better voice quality and it has much more features in comparison.

FEATURES

There's no official feature description for TeamSpeak Classic, so I'll describe myself what it has:

• Receiving and sending voice from other users (using the maximum 640 bytes/s)
• Hotkeys, mute microphone or mute sound overall
• Ideal for dial-up connections
• It comes with no encryption, no text messages, file sharing and Overlays in-game... The only thing it has is voice chats. (Think like an user from 1999)
• You connect to our server, join a channel and there you go, there's no channel password (Although in our server it was set a limit to max 2 users per channel)
• Can be used as a private voice chat, since I bet nobody is going to use it.

 And these are the features... So I'll have other facts in this page, because I don't want them to feel lost and it took me awhile to research about this program.

OTHER FACTS:

• It was made by Niels Werensteijin (Client) and Ralf Ludwig (Server).
• Alternative freeware solution to Roger Wilco back in the day.
  
• There are no Clients for Linux. But it was possible to make Servers for it using Windows and Linux only.
• It was called TeamSpeak Classic or TeamSpeak 1.5 for majority of people back in 2001.

UNCONFIRMED FACTS:

• It might exist a patch for server side for Linux (probably released in 2006) version 1.2.3.

TeamSpeak Classic Official Website (Archive.org)