What do you want to know about Unix filesystems ?
Unix(Linux, MAC, BSD, ...) unlike windows are case sensitive so you can have img.jpg, Img.jpg and IMG.jpg in the same director, *nix filesystem doesn't have drives and separators are slashes not backslashes.
Parameters for executables are given using dash not slash like win and dos.
/usr/share/ is a valid Linux path for example, /mnt/floppy is the standard path for a floppy but it can be changed, *nix executables don't have icons and resources, they are usually assigned to a *.desktop file wich is like a shortcut, Linux uses many links to point to various lib versions, you should always check permissions in a Linux filesystem.
Emulators... sure you have wine, cedega(winex) and wmware, i'm not sure if you have them for MAC.
In Linux you have many filebrowsers wich do not share a common engine so i think you best option would be to make another one instead of interfacing each file browser and set your own file associations, maybe import them from existing browsers.