My favourite part of Opera was Opera Unite. People made fun of it because it was advertised as reinventing the web and stuff like that, but it was really nice. Basically what it did was providing an interface for hosting a webserver in the browser and having a central repository to install extensions for it. There were extensions with simple games, pastebin functionality, webhosting. It was very easy to setup and share stuff with your friend. Sure, you can host a webserver with nginx and install something on it, but it will take you hours or days to setup, while this was instant.