Windows only: Free application Artweaver isn’t just a Photoshop alternative like GIMP,
but a fair clone of Photoshop itself. While Artweaver lacks the polish
and advanced feature sets of Photoshop, the menus are laid out like
they are in 
Photoshop and the tools function close enough that use is
intuitive. The programs are so similar, in fact, that seasoned
Photoshop users will find themselves wondering why a feature is
suddenly missing from the menu. While it isn’t a true replacement for
Photoshop, Artweaver’s feature set is robust; it includes layer
management, image cloning, a history function, transparency, pen tablet
support, and a host of the common filters in Photoshop. Artweaver is
available as a full install or in a portable version. Artweaver is a
free download for Windows only.
thanks lifehacker / cybernet