Yahoo! Messenger was never the most popular, but for many years it was close enough to keep trying, introducing many messaging features years before they became the norm.
ICQ, short for the phrase "I Seek You," laid the groundwork for standalone instant messaging clients when it arrived in November 1996. Think about how long ago that was... Windows 95 was barely a year old, Nintendo had just introduced the N64, and those with a reason to have a cell phone actually used it to talk on.
It was a magical time, PC sales were just booming and if you were lucky, yours would come with a modem for dial-up Internet access. You would hear the scrambling sound of your phone line connecting you to the world. Launching Netscape and staring at the throbber animation while a single web page loaded.