For sending a Reaper project to another Reaper user:
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When you save your project, there are options at the bottom of the "save" window.
-Create subdirectory for project
-Copy or Move all media files to project directory (etc.)
(If your project has already been saved once, and you want to do this function, you'll have to select "save as" from the File menu.)
Then I'd recommend going to the File menu again and use the "clean current project directory" function (to remove items you've deleted from your project but which remain in your project folder).
Then your project is all contained in one folder along with the .RPP file. You can zip/rar/whatever the directory and send it to your friend, and he can open/edit it in Reaper. If he has a different audio device at a different sample rate setting, or doesn't have the same plugins you have, he'll have to compensate. I think the sample rate of the project (which is saved with the project) will override his audio device's settings by default. But you might want to tell him in advance what sample rate you're using, in case he has to change settings. If a plugin is missing, Reaper will mention it when opening the project and also give indications of it in the effects slots, with "!" shown (and in red or something) by the missing plugin's name. If he wants to install the missing plugins he can, then restart the project, and Reaper will have it figured out.
For sending files to another application which isn't directly compatible (Pro Tools etc.
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-Select the tracks you want to export. They'll be exported as WAV, AIFF, or whatever you choose in the next dialog.
-From the render dialog (under File menu), choose "Render: stems (selected tracks)".
-Check the other options in the dialog before you render. There are a number of things to consider and it depends on what program you're going to open it in, what sample rate you want to work at, etc.
Now you can import those media files into the other application starting at time 0:00. (Do this however it makes sense to import files in the other application.)
Recommended before you do the above three steps:
-Presuming the project were done to particular tempos and time signatures, and you kept proper time to it (if this isn't a "seat of your pants" performance), you'll want to make notes of the tempos and time signatures (and where the changes occur). You can also create a "click track" in a couple different ways to include with the other "stems", including a "lead in" measure or two with the opening tempo/time signature. (That's something I'd recommend.) Check this video:
https://www.youtube.com/watch?v=GnEFzM4zJsM
So, that becomes a track like all your others, containing the metronome click. And you can export it along with the other files. That will prove valuable in most situations.
I don't know if MIDI files get exported in this process. I've never done that since it's never come up, the way I work.
-Also: name your tracks before this exporting process. The names of the "stem" files will be based on the track names. If you don't name them, somewhat arbitrary names are applied. It's easier to import and organize files named "guitar L", "guitar R", "drum - kick", "drum - snare" etc. than it is to import and organize a bunch of files with names like "345_tk5_001.wav"
Good luck!
