Haven't seen this one receive a mention yet:
TagSpaces:
https://www.tagspaces.org
From the Website:
"
What is TagSpaces?
TagSpaces is a new, cross-platform tool for organizing, editing and tagging information.
What is it good for?
Users can operate with local files and folders on different platforms through a single friendly interface which allows them to view, edit, and add tags to their information.
Is it compatible with my platform?
It is compatible with Windows, Linux, Mac, Android, IPhone, Firefox and Chrome.
Do I need Internet access?
No
Is it a cloud service?
No
Where do I register my account?
Nowhere
Does it use database for saving the tags?
No
Is it secure?
The app makes no external requests, it’s completely offline, all your data is stored locally and never sent by network. It doesn’t contain any statistics collection scripts, analytics or ads. The only request this application performs is version check which can be disabled in the settings.
Where does TagSpaces save the tags?
Currently the tags are added in name of the file, so for example if you tag the file “img-9832.jpg” with the tags “sunset” and “bahamas” it will be renamed to “img-9832 [sunset bahamas].jpg”. A version of TagSpaces which saves the tags in a sidecar files will be released soon."
Portable Mode introduced from the release of Version 2 - see
https://www.tagspaces.org/blog/tagspace ... rtablemode
I haven't tested the claimed portability yet, but thought someone might be interested.