I'm putting together a page of resources and tools that I think will aid game developers. I'll be updating as I find more resources so please check back continually. These are not restricted to free resources although they are added with the spirit of indie game dev in mind so I'll try to avoid adding expensive industy standard sorfware, like maya and photoshop etc. If you have a resource which you think will be useful for developers feel free to let me know and I'll add it to the list. The first list on the page is for resources which will help you modify my assets from the site.
Resources for working with assets from this site
Inkscape
A free and open source vector graphics program. Use this program to modify assets downloaded from this site.
Krita
A free and very powerful painting software similar to photoshop but without the price tag!. I recomend for raster editing.
Texture packer
Software for trimming down textures, creating texture maps and much more. Necessary if you're using animations from the site.
Brash monkey spriter
Animation and tweening software with a limited free version and a more comprehensive yet affordable pro version.
Tiled
Free and easy to use tile map creation software for building levels. Supports orthogonal, isometric and hexagonal.
Bosca Coil
Online or offline (as dowload) easy to learn music and sound creation tool. It's also completely free and you can start right away.
audacity
Use this or chopping triming and putting together your sound effects and sound clips