Exciting news! I've become the owner of Seamless Texture Generator which is a great tool for making tile textures for games (and other stuff) out of images. It work really well and part of the reason I bough the IP is because of how well it works. Here's an example:
Notice how even the jarring seem created by the cement bag is smoothed away.
See for yourself, there is a free demo: http://www.seamlesstexturegenerator.com/
The program is pretty old and doesn't support Windows 10, but I'm hoping to write a new version down the road.