Replacement for Picasa that respects my folder layout

Question

Now that Picasa is being retired, I'm looking for an alternative with the following features:

1. Works on both Windows and Mac OS. (And, for bonus points, Linux.)
2. Allows me to organize my images my way, in folders on my hard drive. (Most apps store your files in a proprietary database format that locks you into using that program.)
3. Allows me to easily search and browse my photos, and add metadata like tags and descriptions.
4. Stores as much of that metadata as possible in EXIF tags in the image (again, I don't want to lose metadata if I have to switch apps. I have currently tagged my images using Picasa, with the tag info stored in the image files themselves.)
5. It'd be nice to be able to create Albums like in Picasa, but failing that, simply tagging a group of images and being able to quickly search for every image with that tag basically does the same thing.

Free or inexpensive would be a nice bonus.

Answer 1

After extensive research and searching, I've found the open-source tool Digikam meets all my requirements and many more - it's a very impressive tool.

1. It works on Windows, Mac, and Linux.
2. It respects your folder structure, like Picasa. It even allows you to have photos on external storage that might get disconnected, and network shares that might have poor performance, and handles these specially.
3. It allows browsing by folder or tag, and searching by any metadata.
4. It stores tags, titles, captions, and other data in the image files themselves.
5. In digikam, the word "Album" simply refers to a filesystem folder. Tags, however, can be used to group photos, and searches can be saved as "Virtual albums" - either can be used like "Albums" in Picasa and other tools.

It has quite a lot more features, too.

Limitations:

1. Digikam seems to lack a "Reveal in File Manager" command, which seems to be standard in every other media management tool I've ever used.
2. There's no way to manually re-order the pictures in any digikam view, as you can in Picasa albums.