This version is a maintenance release with a new "Allow multiples instances of Atlantis" option on the General tab of the "Tools | Options..." dialog:

When this option is off, only one running instance (copy) of Atlantis is allowed. For example, when there is a running instance of Atlantis and you double-click the Desktop shortcut of Atlantis, no new instance of Atlantis gets launched, but the already running instance of Atlantis gets activated instead. For more info on this new option, please click here.

Another change in this version is that Atlantis can now automatically save its current settings at regular intervals against system failures. Previously Atlantis only saved its settings on close. Now, if the "Safeguard every NN minutes (against system failure & crashes)" option on the Load/Save tab of the "Tools | Options..." dialog is on:

Atlantis not only creates safe copies of all unsaved documents, but also automatically saves all its current settings at specified intervals.

See more release notes.