GimPhoto is an interesting image editor which markets itself as a free alternative to Photoshop. While it may not offer everything Photoshop has, it's certainly an impressive image editor. GimPhoto Portable is a portable version of GimPhoto which you can take anywhere with you on a USB stick.
GimPhoto is heavily modeled on GIMP except by default, it already includes 20 GIMP plugins that make it as close to Photoshop as possible. If you've used GIMP therefore, you'll feel very at home with GimPhoto. One of the frequently cited problems with GIMP is that the interface and menu labels are a bit confusing and awkward compared to Photoshop and this is certainly something that GimPhoto has improved upon.
GimPhoto incorporates many of the features of GIMP but with an improved interface, batch processing, online backups, custom brushes and advanced editing options. The menu layouts are much closer to Photoshop meaning Photoshop users will adapt to it much quicker than the GIMP. However, it's still a quite complex package although there's a very detailed user guide to help you get to grips with it.
GimPhoto is an impressive attempt at making a free version of Photoshop and if you never really adapted to GIMP, it may well be the image editing package for you.