While this feature has been on the forum for a while now, I never actually used it. But let's make it official - this forum now supports Discord widgets.
Discord widgets are a way to invite people to your server without generating an invite link. Prospective members get a small overview of who is online in your server and get to see the server's name.
Some rules: (sorry, yes we need a few)
1) This is only to be used in the opening post of a project thread, or any thread that is directly relevant to the server in question. I.E. if you want to discuss 3D Realms' Discord server and you made a thread about that, you could post their widget there.
2) Please do not post others' widgets without their permission, if it's a private server.
3) Any sort of widespread abuse of this tag will lead it to be taken away. Don't be a rotten apple!
In order to show a widget in your post, first you need to enable it, then you need to get your server ID. Then stick the ID inside the [discord] tag - i.e.
Here is an image along with step-by-step instructions:
1: Enable the widget if it is not already. Right click your server, and go to "Server Options" (or "widget" if you see it), then navigate to the widget tab. Then push the slider to the "on" position.
2: Set your invite channel. The widget creates faux invite links that it will use to direct your new members. It is important to set a channel that you would prefer them to see. (Often this can be some sort of introduction, a rules page, etc)
3: Finally, copy your server's snowflake ID with the Copy button as shown in the image above.
Then, put the snowflake id inside the Discord tabs as shown in the example above the image above. And you're done!
If everything worked correctly, you should get a working Discord widget, like so: