1997 Digital TCG
Chron X was released in May 1997, and holds the Guinness World Record as the first digital trading card game that let players actually own and trade their cards.
The servers were taken offline many years ago, but the client supports peer-to-peer play. (How very, very 1997.) Here's how you can play, right now.
The game client and two testing game accounts can be found here. Download and use of the game is governed by the Chron X End User License Agreement.