Module request: content lock

Often requested by content managers, this now has a 2.x release and an active maintainer:

https://www.drupal.org/project/content_lock

• Block concurrent editing: When a user is editing a node, any other user that attempts to edit the same node will be blocked from doing so, and notified that the content is already being edited.
• By node type: This module can be configured to only lock certain content types against concurrent editing.
• By format: This module can be configured to only lock specific input formats against concurrent editing.
• Avoid losing content by accident: If a user is editing content and attempts to leave the edit form without first saving it (e.g., closing the browser window/tab, clicking on a link, etc.), they will be notified. If the user confirms that they want to leave without saving the node, the edit lock gets automatically removed by an ajax call. This behaviour can be disabled on the modules settings page.
• Avoid forgotten locks: Users are notified if they forget to unlock a node. They will be prompted to click on a link to unlock the node.
• Views integration: All open locks can be listed using Views.