Tamriel Rebuilt, Project Tamriel building unified Data Structure
Starting with release 1609, Tamriel Rebuilt will move to a new data structure. TR_Data is out, Tamriel_Data is in, and a host of changes come with it!
If you just want to skip ahead, you can find download links here.
Culminating from a year of hard work, Tamriel_Data contains a unified file structure spearheaded by Project Tamriel and Tamriel Rebuilt as the first adopter.
Not only will this make assets from both projects available to each other and third party modders, but the assets are organised in a logical, easy to navigate syntax, enabling our modders to create content more easily. A file name will now have the context that was previously only known by trial, error, and experience.

It will probably not quite look like this.
Additionally, we are now supplying both vanilla-style resources and a high-resolution alternative. Now, no matter how much you doll up your game, mods relying on Tamriel_Data will never look out of date again!

Left: low resolution, Right: high resolution
Note: While the assets for Project Tamriel are all available in both high and resolution, Tamriel Rebuilt is not nearly done. Any texture artists willing to help are welcome!
Tamriel_Data for players
Update your BSA list
First, if you used more than one of the big three province Mods (Tamriel Rebuilt, Skyrim: Home of the Nords, Province: Cyrodiil), you will be able to just use Tamriel_Data with each of them. Three ESMs and BSAs now become one ESM and one BSA: easy on the load order, and easier to keep track of.
The hardest part is remembering to edit your Morrowind.ini to use the new BSAs instead of the old ones. Since you have probably played one of the bigger mods, you should know how this works: just locate the file in your Morrowind game directory, find the [Archive] section, add the two new BSAs (TR_Data.bsa, PT_Data.bsa), replacing obsolete entries if they were there, done.
Alternatively, you can of course use BSAReg, which ususally takes care of that automatically.

Example setups
Just make sure that your Tamriel_Data is up to date, which the province mods will alert you to in our releases.