At this time it’s not possible to collaborate on shared Entries or Journals within Day One. That said, you can share individual entries outside of Day One by following these steps:
iOS
There are a few of ways to share entries to other applications.
Tap the More icon (•••) at the top right of an entry. Choose Export. This will open the share extension view for options to send the entry.

- Swipe on the entry in the Timeline view > tap the More (•••) icon > tap Share.

- There is a Share/Export option in the Entry Info/Metadata menu.

macOS
Enabling the Day One Share Extension
Follow these steps to enable the Day One Share Extension:
- Go to Mac System Preferences > Privacy & Security > Extensions > Sharing.
- Find Day One.
- Click the checkbox to enable the Day One share extension.
- If desired, click and drag Day One to move it to the top of the list. This will make Day One the first item in app share menus.

- Right-click on an entry in the Timeline view > choose Share > choose the desired destination

- While viewing an entry, click the More icon (•••) at the top right > click Share > desired destination

Android
Tap and hold on an entry in the Timeline view, then tap Share.

While viewing an entry, tap More (•••) at the top right and then tap Share.
