Gemini
The gemini protocol is an alternative communication protocol to options like HTTP or gopher. It is currently considered feature complete and works quite well.
Gemini is a protocol heavier than gopher, lighter than the web, aims for high power to weight ratio, takes user privacy seriously and isn’t looking to replace either gopher or HTTP. They have an FAQ answering many common questions. It would be fun for me to go on about the protocol but the wiki and the FAQ have pretty much all the information you could want to know about this so please just spend a little time browsing the site.
Clients
There are a number of clients to choose from. I use castor. The clients and in some ways the protocol follow the UNIX philosophy well. For example, this site has photos on it but it doesn’t load the images within the browser. I need to click the button for the image, my machine will download it and open it in my default image viewer. Some things like this are debatable though. Some argue it is worse for user experience or that as long as the image rendering is done by the same program in the background, it still sticks to the UNIX philosophy so the way it is currently is unnecessary.
You can still access gemini sites with proxies on normal browsers instead of having to install one of these clients. Browser extensions exist too to automatically proxy gemini links.
Conclusion
Gemini is a very simple protocol and for specific circumstances, I think it is a very good protocol to use. With how big HTTP is now, it will be interesting to see the popularity of gemini over time and the kinds of people that will use gemini.