Kristall - A nice all-in-one SmolNet browser, supporting Gemini, Gopher, Finger and even text-only HTTP and HTTPS websites.
wApua - The only WML browser that works on modern systems. Even then, Linux only.
Gerbil - A Gemini and Spartan Protocol (Not to be confused with The Spartan Web) Browser
Wayback Machine (iOS | Android) - Not as good as TheOldWeb browser, but this is another okay option for exploring archives websites
Ecosia - Not the most privacy focus engine, but it does plant trees, giving you a peace of mind that you're doing a wee bit to help stop or at least slow down Climate Change
Matrix (Fluffy Chat | Nheko | Element) - A nice, federated chat system that has good chatrooms to hang out in, and some are even bridged to Discord!
XMPP (Dino | Yax.im | Monal) - Another decent federated system. Used to be used by all of the big names, Skype, Facebook, AIM, Google Chat, etc., but those have gone proprietary since, but the open system they used to use remains, and is still active.
Syncterm - A modern BBS browser. Yes, they're still a thing, and it's glorious!
Newsgroups - Newsgroups are also still a thing, but aren't as active as BBSes or XMPP, but you'll see some communitys going about. I use Thunderbird to access them.
Fosscord - An in development client that can connect to the Discord protocol, allowing you to still access Discord servers and contacts without putting up with Discord's garbage. Fosscord is using white-box cloning to achieve this, which is legal in both the EU and US. This means, in theory, they're doing nothing wrong, and Discord can't do anything about it.