I've been on the lookout for an app filling these requirements for quite a while, so I figure I will just write my list all in one place.
- Open source and actively developed
- Allows saving tags directly into photo files (it's okay if this is configurable and not the default; usually the default in such apps is to save metadata into the tool's own special database)
- Allows searching by tags
- Has a GUI (i.e. ExifTool won't do)
- Must run on Linux
Really really desirable but not absolute musts:
- Allows tagging videos as well as photos (also with the tags saved directly to the files), and searching videos
- Can navigate the filesystem without having to "import" photos first
- Can have keyboard shortcuts set up for tags to be applied to photos/videos, making it easy to do this singly or in bulk
- Runs on both Linux and Mac
"Nice to haves":
- Can be used to set up "collections" of photos (or any files, really) without moving the files' positions on the filesystem
- Can have "smart collections" set up with essentially saved searches
(Incidentally, ALL of these points except for "open source" and "runs on Linux" are fulfilled by the proprietary, gratis application Adobe Bridge. But I'm trying to move from Mac to Linux and cut proprietary applications out of my workflow.)
By the way, I don't actually care if the app can edit the files or not in terms of photo editing/color correction/etc. I just care about tagging and searching, and maybe rating (which I count in with tagging).