Those who follow along the development of TM know that changes are typically installed on
https://tmtest.teresco.org to give people a chance to check on/make suggestions/report bugs before new code goes up on the main site. There was also a tmtest2 that I rarely used. The problem I've encountered is that tmtest plays the role of both development and staging server, and once in a while I clobber a change I've asked people to test as I'm developing something else myself.
To add flexibility to this setup, I now have three such servers:
https://tmdevel.teresco.org will serve as a development server that I will feel free to modify and break as I see fit when developing code. You're welcome to check it out, but it's not likely to be of use to anyone other than me.
https://tmstage.teresco.org will serve as a staging server, where I will direct people to check out new features (as I have been doing with tmtest).
https://tmtest.teresco.org will be available for other testing needs, such as how it is being used today to try out a change that needed a configuration change to load data from an alternate database. I can also use it if there are two distinct changes in development concurrently and it makes sense to stage each on its own server.