This was also true on the comms apps sides. Back in the days of ICQ & Jabber, there was a huge ecosystem of chat apps, many of which (like my favorite, Miranda IM -- which has been revived for Windows as Miranda NG: https://miranda-ng.org/about/) were also fully customizable.

I remember how "true" guys did their own Miranda from scratch (which as I remember even ICQ or Jabber was needed to be installed manually as plugins). But most of us (me also) used ready builds, which was also awesome