Matrix is a decentralized protocol used for chat. I am on there often, so you can use it to raise me for quick things. (It's not always instant, but it's usually quicker than email).
Matrix users have accounts on different instances. The identifier for a matrix user looks like this @<username>:<instance-name>. For example, mine is
You will sometimes see a matrix identifier as a link targeting matrix.to. That is a way to quickly raise the user if you already have a matrix account, or to sign up for an account on an instance if you do not. There are two ways to sign up, depending on your relationship to me:
Way 1: You know me, work with me, or are a student in a course I'm teaching
You should send me an email about getting an account on my instance, llllllllllllllllllllllllllllllllllllllllllllllll.space. You cannot register through the website; I'll have to do it for you. But once you have it, you have it for as long as you'd like, and you can communicate with a lot of services using it if you so choose.
Way 2: You mostly don't know me
If you click my matrix.to link, @david:llllllllllllllllllllllllllllllllllllllllllllllll.space, you'll be taken to a page that asks you to "choose an app to continue." The simplest thing to do is to choose Element, and then choose "Continue in your browser." That will take you to a "preview" that shows what chatting over matrix with Element is like, but with none of the text filled in. Just click "direct message" and you will be prompted to create an account. If you select "sign up" you'll be taken to a page to sign up for an account with matrix.io. Do that, and follow the instructions to sign in. Once signed in using element on the web, clicking the matrix.to link will allow you to message me, add me as a friend, and so on.