Photoshop alternatives:
- krita - Windows, Mac, Linux - resources/tutorials/examples - This is VERY impressive
- GIMP - Windows, Mac, Linux
- Fire Alpaca - Windows, Mac
- SketchBook Pro - Windows, Mac
Illustrator alternatives:
- Inkscape - Windows, Mac, Linux
- OpenOffice draw - Windows, Mac, Linux
- LibreOffice draw - Windows, Mac, Linux