I really like skeuomorphic UIs and early 2010s UIs, because they look nice and generally, they tend to be more space efficient than modern UI. This is a thread for themes/plugins that make modern programs/websites look that way.
I'll start:
- SkeuoCord is a skeuomorphic theme for Discord, it doesn't change the layout but it makes icons/backgrounds have that iconic gradient most early 2000s-2010s interfaces had.
- YouTube Redux is a browser plugin (Firefox version) that lets you restore YouTube's layout to how it was years ago. I find this really useful because the old layouts were much more space efficient than the modern ones.