Update: Bullroarer has been up this weekend, and will likely be up on weekends until they are ready to launch.
They are starting to test Update 21, the Mordor Expansion Pack, on Bullroarer. If you're interested in seeing what's coming or just want to try some things you can't afford on the real servers, you can download the Bullroarer client and check it out.
The Bullroarer server will be up from time to time as they test out the new content and other changes. To access it, you must download and install a separate LOTRO client, which is around 24 gigabytes. You can keep both clients on your computer and switch back and forth between the Bullroarer client and the regular client, but an account can be logged on to only one server at a time (either Bullroarer or one of the real servers). You can copy one or more characters to Bullroarer using the transfer feature. What you do on Bullroarer does not affect the real servers, and there's no way to get anything back from it. On Bullroarer you can get lots of gold, LP and MC to spend, as well as other tokens and barter currency. There are ways to instantly level-up new characters.
The Bullroarer forum https://www.lotro.com/forums/forumdisplay.php?787-Bullroarer-(Public-Test-Server) has a lot of information, although it's not always easy to find.
The download links are here: https://www.lotro.com/forums/showthread.php?571061-Bullroarer-client-Installer-DOWNLOAD-LINKS Note that if you have installed it before, you should not need to download it all again. If you start the Bullroarer client, it should update to the current beta version just like the normal client does.
As of this moment, they have not yet updated Bullroarer with the first beta update. However, you can download and install the client if you don't have it yet, or update your Bullroarer client to the previous beta to reduce the time to update to this beta when it is available.
I will post further messages on this thread as we get more information. If you have questions, let me know.
As always with Bullroarer, things may change before it goes live.