Tessa's brother Nicholas Sherlock has made a variety of programs for use with the Petz/Babyz games including:
PetzA - provides you with the opportunity to force instant pregnancy/birth and choose the litter number, take out unlimited petz to play together instead of just 2, use brainsliders to control all aspects of your pets health and much more. This program also works for Babyz.
LNZPro - LNZ Pro is an all-purpose Petz, Babyz and Oddballz file editor. It can edit breeds, pets, babies, toys, playscenes and other Petz resources. It is a complete replacement for the tool "Resource Hacker", without the bugs! This program is a must for hexers.
Tinker - A program which makes easy work of creating new toys, clothes etc
Pet Workshop - Edit your petz in a 3D editor - so you can see exactly what you're doing when you're hexing! Comes complete with tattoo files to make hexing simple
Please take a moment to check out his website Sherlock Software to download these and other great programs for free!