As far as I am aware the only other PF/Mac reader for Adobe DRM is Sony Reader; free download from Sony intended to run with Sony eReaders but works quite happily without. I prefer ADE1.7.2 to Sony Reader. https://ebookstore.sony.com/download/ I do not think it will help with syncing annotations.
several choices I can suggest for you to weight up for your situation.
1 ~~~~~~~~~~
Are you using a ADE on a computer at both ends for reading/annotating? (eg, no tablet or eReader device involved).
Assuming computer at both ends, you could use standard syncing software to sync from the Adobe Digital Editions directory (typically Documents\My Digital Editions) to a directory on the pendrive.
When finished on a machine, make sure sync to the pendrive runs, and then when starting on the other machine make sure sync to the pendrive runs. The data will live on both machines and the pendrive.
2 ~~~~~~~~~~
If you are fairly technical, you can make a directory link (one on each machine) so that the Documents\My Digital Editions directory links to the pendrive. This will be more convenient, but the pendrive will be the only place your data lives unless you make other backup arrangements.
3 ~~~~~~~~~~
If you have access to a cloud syncing service such as Dropbox or Google Drive at work, you could make a directory link (one on each machine) so that the Documents\My Digital Editions directory links to the appropriate folder, The data will like on both machines and the cloud; this should be both convenient and good against failure.
4 ~~~~~~~~~~
Some cloud syncing services will allow you to sync more arbitrary directories so you wouldn't need to worry about linking directories. I can't remember which ones right now ~ I may post back with a suggestions.
If you are technical enough to want to try directory linking as in 2 or 3; but not sure exactly how, post back and I'll add more detail.