Opera Mini was first released in 2005 as a web browser for mobile phones, with the ability to load full websites by sending most of the work to an external server. It was a massive hit, but it started to fade out of relevance once smartphones entered mainstream use.
Opera
I used this! It was a godsend for people like me on a metered MVNO plan with only access to 3G towers and no home Wi-Fi (when you’re extremely poor, you make sacrifices).
That’s cool that it’s still available, and I bet there will be a resurgence of dumb phones in the coming years that would be glad to use it.