As I mentioned earlier here: https://happyts.tech/history-of-sync-tool/ AAD Connect has its root in FIM / MIM.

During the way of evolution to the current release of AAD Connect there were several steps:

Azure AD Connector for FIM this is an extension for FIM and works also with MIM (see further information here: https://docs.microsoft.com/en-us/previous-versions/mim/dn511002(v=ws.10)?redirectedfrom=MSDN)

The next version was a downloadable version of a customized FIM with the version: 4.3.647.0 was called WAAD Sync:

So far I remember this was special version what could be downloaded from the Office 365 (BPOS) Portal.

As you can see this suggest, that this is a MIM Version, but if we have a look on the MIM version release history page we can’t find this version there:

The MIM release history can be found here: https://docs.microsoft.com/en-us/microsoft-identity-manager/reference/version-history

So this is a kind of pre-release of DirSync (https://docs.microsoft.com/en-us/azure/active-directory/hybrid/reference-connect-dirsync-deprecated)

The next version of the sync tool was AADSync with the version number: 1.0.419.0911 this was released in Nov 2014 (https://docs.microsoft.com/en-us/azure/active-directory/hybrid/reference-connect-version-history-archive#104190911)

The first version of AAD Connect was released in June 2015 with the version number: 1.0.8641.0 ( https://docs.microsoft.com/en-us/azure/active-directory/hybrid/reference-connect-version-history-archive#1086410)

This is only a short overview only for informal purposes. I recommend to use the latest version of AAD Connect (currently 1.5.45.0). You can find the release history and the url to download the latest version here: https://docs.microsoft.com/en-us/azure/active-directory/hybrid/reference-connect-version-history

Happy Troubleshooting!