@jessegrosjean I somehow opened a document and created a new one within the same window in a new tab. In that window when I create a new document, Taskpaper opens a new tab with it.
I really love that feature, but I haven’t been able to reproduce that in my other computers. Not even in the same computer in a new window. What am I missing?
Update: I see that I can do it if I click on “Merge All Windows” within the “Window” menu. Is there a way to do it without having to click on that?
This is a new macOS 10.12 feature that TaskPaper gets for free. I’m still on 10.11 so haven’t had much time to experiment with it and am not sure about the options.
Just let me tell you that it is AWESOME!. I really thought that you implemented that somehow and I missed the announcement.
When you are in “Full screen mode” and create a new document, the new document goes into a neat little tab. It only occurs when you have the app in “Full Screen”. Outside of “Full Screen” you can stitch your windows together by the “Merge All Windows” option as I mentioned above; but the tabs are only added automatically when creating a New Document in “Full Screen”. It might be easy to add a new “Add new document in a tab” option in Taskpaper later on 
. Have a good one.
+1 on the ability to open discrete documents in separate tabs in a single TaskPaper window. I have things organized into home/work/etc lists (separate documents). It would be very convenient to keep them all open under a single instance. — Nathan
This should be possible now in 3.5 if you are on macOS 10.12.
That should do it. As long as you quit TaskPaper without first closing that window the merged windows should restore automatically next time you open TaskPaper.