DescentBB

So it's been years. I just installed d1 and d2 rebirth.

Where can I find multiplayer games? Where to people go to organize them? Are there trackers? Do they still use Kali (or whatever is was called)?

For D1 and D2, Kali is probably still the best route. There are also some sticky threads in the Descent Multiplayer forum that might help you.

Not many people do use Kali, though there are some that do, including some that may not be reachable any other way.
There are trackers: both major source ports have them built-in. I don't think the D2X-XL tracker is visible to the web at the moment - but it's had one for quite a long time. Rebirth gained one within the last couple years as well which can be seen here: http://dxxtracker.reenigne.net/

Outside of Kali, there are a couple places I can think of to find people for games (may be more out there though) - both hosted Mumble servers.
Rebirth server: dxxr.mine.nu:64738
Descent Rangers server (seems more active lately in my experience): vx39.commandchannel.com:31393