Issue Checklist app supports simultaneous editing of the checklist in multiple windows of the browser.
This way more users can work on the same checklist at the same time.
Adding new item, toggling an item, editing item's summary or recording items in one window does not overwrite concurrent actions performed in the other windows.
Only the same action performed on the same item can get overwritten, e.g., modifying the text of the same item in a different window.
Changes made in one window become visible in other windows when any checklist action happens in those windows (e.g., checking an item gets and displays the current checklist with changes from other windows).