Stem Manager

Stem Manager is free, but if you find it useful, please consider paying.

Reaper is very flexible when it comes to render options.

Still, exporting stems is a chore -
1. It usually requires a lot of pre-planning.
2. It is often impossible to do without requiring signal flow changes or compromises.
3. It's especially hard to make multiple sets of stems containing the same tracks in several unrelated stems, making sure all send FX are rendered for only the selected tracks.
4. A lot of things need to be verified or re-made before each export.
5. It often needs re-doing on every project.

Enter Stem Manager!

Stem manager allows easily creating stems by saving and recalling multiple sets of solo and mute states, running different sets of rules and actions for rendering those stems, and either adding them to the render queue or rendering them consecutively (avoiding the need to reload the project between each render operation), all in a simple interface.

For example - some stems need to be rendered from a bar-line with a certain render preset, while others from the audio start point with a different render preset.
Some render presets require making sure specific regions are selected before rendering, while others require making a specific time selection. This is easy to do in Stem Manager, as well as selecting markers for Reaper's recently added ability to render between selected markers!

There are many more render rules available, and if that's not enough - custom actions can be run before and/or after rendering.

While setting Stem Manager up is a breeze, all settings are saved with the project, so they can be a part of a project template for easy recall.

Tracks save their stem assignments as part of their "chunk" which is also included in track presets. That means that loading a track preset which is part of a stem to a new project will create that stem in the new project and assign the track to it! For example, a "guitar bus" track preset will always be a part of the "Guitars", "Playback" and "TV Mix" stem, if defined that way.

Additionally, custom actions can be easily exported to the Reaper action list to trigger behaviors from anywhere within Reaper using shortcuts (or any other remote control method Reaper supports), even when the script isn't running!

Stems can also be "mirrored" - meaning the project will reflect the stem's solo and mute states in order to audition what the stem sounds like.
This, with the addition of the custom action, makes Stem Manager a convenient solo/mute groups toggle tool as well.

There's a lot more to cover, and you can see everything in the video up above.

For questions and comments, please go to the Stem Manager thread at the Reaper forums.