What's the most popular portable applications manager?

UpdateNotifier is probably not a portable applications manager.

But, it helps track updates on your freeware.
It scans installed applications and checks for updates.
I like its small footprint, and fast interface.

The site also enumerates another popular applications list based on these stats.

LiberKey - Automatic online update of Portable Apps: the launcher programs scans update for ALL the installed apps. Furthermore, it will download AND install them automatically for you.

http://zia.blogspot.com/2009/06/liberkey-automatic-online-update-of.html