HolonPlus includes atomic version control.
A version button in the status bar displays the current version number. The adjacent entry field provides space for a description of the current change, as a steady reminder.
Edited items are tagged with the current version number. If the item has been changed, the previous version is moved to the list of old versions.
You can look up a previous definition by clicking on its version number in the title pane.
A right-click on the version number shows the units that are involved in that revision.
Old versions remain in the project database until the database is pruned at a milestone.