512 Pixels wrote an intriguing piece on the Apple Jonathan, a concept computer from Apple in the 1980s:
This concept envisioned a computer that would expand with the needs of the user, through the use of modular components […] A small team worked on the concept for about eight months before engaging Frog Design — yes, that Frog Design — to work on a prototype design to show the idea to Apple brass. […] The general idea was simple, but in practice, this machine would have been a nightmare. The backbone of the system would need to accept modules from Apple and other companies, letting users build what they needed in terms of functionality […]
The post also shows a ton of images, both real and rendered by enthusiasts. As said above, it looked cool but it was very impractical.