I found this Photoshop competitor on the web.

Pixelmator.

http://www.tuaw.com/2007/08/09/tuaw-exclus...pth-screencast/

This is a short video about the app, and some info.

Only for Mac.

I wouldn't call Pixelmator a Photoshop competitor. They are simply not in the same league (features & price). As far as I know, Pixelmator is based on Apple's Core Image framework. You can get a pretty good idea of Core Image functionnality if you have the developer tools installed and play a bit with FunHouse (Developer>Examples>Quatrz>Core Image) application. Core Image is GPU dependant so you'll need a good video card to get decent speed.

We'll get a clearer idea of Pixelmator once it's released...

The thing is, that I need some application to design my promotional cards. So far I only have the option of getting pages.

Photoshop's price of 1000$ and the learning curve (I need them now, not in a month) makes it impossible to use that application.

Have you tried something like Graphic Converter (here)? Or you could try LiveQuartz (here). Like PixelMator, it also draws much of its functions from Apple's Core Image framework.

Thanks, Francois. Can I actually design postcards with these applications? Can they do CMYK conversions?

I think that you can probably design postcards with these products but I doubt that any of these applications can output CMYK files. LiveQuartz is free and GraphicConverter works as a full-feature demo so you might want to try. I haven't seen if PixelMator supports CMYK conversion.

You could also try to download Caffeine Software applications (here). The company is dead but its software is still available for download. TIFFAny might offer what you need but, as far as I remember, the interface is weird and non-intuitive and I never had the nerves to try for more than a couple of minutes.