Various online craft tools exist, usually for colour planning or design generation. These are the ones I know about:

Needlework

Cross Stitch Charts from photos

My Photo Stitch a free service that takes photos you upload and gives you a cross stitch chart using (last I checked) DMC colours

Knots

Turk's Head Cord length calculator

http://turkshead.50webs.org/

Turk's Head Knot designer

http://data.oreilly.com/jallwine/knots/

Globe Knot Core Calculator

http://khww.net/gkcc.php

Kumihimo Braiding

8 strand kongo gumi colour planner

http://www.lythastudios.com/123bead/kumiplanner.html

16 strand kongo gumi colour planner

http://craftdesignonline.com/kumihimo/

A colour planner for the 7-loop Spanish finger loop braid

http://www.islandlife.heliohost.org/cgi-bin/fingertips.pl

Weaving

Card weaving design planner. Online or downloadable.

http://www.theloomybin.com/cw/

Design weave structures and colour compositions for handweaving.

http://www.theloomybin.com/loom/

Lace

Lace: knitted lace designer

http://www.unikatissima.de/shop/?page_id=494