This is a Zbrush Ztool that I've specially set up to be super easy to sculpt tiling textures in conjunction with the WrapMode setting. It has a subtool to help frame your tile perfectly on the canvas when you press F, and uses a texture that you can set to mask out the range beyond the tile. You can adjust the texture masking under Texture Map > Transparency. Alternatively you can just turn the texture off.
I have also included a handy-dandy macro that will duplicate and offset extra subtools automatically (think the offset filter in photoshop) to make sure that any extra subtools you add to the tool will tile properly when baked to a texture.
Video walkthrough of the tools
Updated user license for commercial use