2D Tools

Krita – Open Source digital painting and illustration application
https://krita.org

GIMP – GNU Image Manipulation Program
http://www.gimp.org
http://portableapps.com/apps/graphics_pictures/gimp_portable

Artrage
https://www.artrage.com

Escape Motions Rebelle – watercolor, acrylic, dry media
http://www.escapemotions.com/products/rebelle

Mischief – vector beziers and curves with infinite canvas
https://www.madewithmischief.com

Paint.NET
https://www.getpaint.net

Corel Painter
http://www.painterartist.com

ABRView (Photoshop .abr viewer)
http://www.easyelements.com/abrview.html
http://sourceforge.net/projects/abrviewer

FotoSketcher
http://www.fotosketcher.com

CamStudio – Free Screen Recording Software
http://camstudio.org

NVIDIA Normal Map filter – Plug-ins for Adobe Photoshop
http://developer.nvidia.com/object/photoshop_dds_plugins.html

RealWorld Icon Editor – Free Icons and Cursors Editor
http://www.rw-designer.com