GIMP is the closest FOSS app to Photoshop, and I believe it can read
layers from a PSD file, though very Photoshop-specific effects like
adjustment layers won't work, and I don't think text layers retain
their text information. Likewise for going the other way: don't
expect GIMP to be able to save all its info to PSD format. Keep in
mind that PSD isn't an open or well documented format, so the
PSD reader/writer in GIMP is mostly just whatever some developer
has been able to reverse engineer. That said, you should be able
to read basic layer information.

        ...Akkana (who wrote a book on GIMP some years back but hasn't used PSD)

LeRoy Diener writes: