WRT clothing pattern software, you asked "Do such tools exist?"

And I can only respond with "They don't need to."
While technology such as CAD software and laser cutting machines can
certainly assist the Maker of Clothing with making things *faster*,
the only tools *required* for creating clothing are a flexible
measuring device of some sort (usually a tape measure) and a pair of
scissors. Everything else is just gravy.

Think about it: It's only in the last 200 years that the Common Person
has become acclimated to this idea that clothing is something made
outside of the home. Prior to the Industrial Revolution almost every
item of everyday use was produced by family members, many of whom were
not only illiterate but had no formal education in arithmetic or
geometry. Sure, there've been Specialist Tailors for at least 1000
years who would produce out-of-the-ordinary or high-end "couture" for
those who had the money to pay, but in general your wife, your sister
or your mom produced your day-to-day clothing. With no training beyond
what they in turn learned from other family members.

As a former Fashion Student, I can assure you that anyone can learn
not only basic clothing-assembly techniques, but also the craft of
draping a three-dimensional human figure with two-dimensional pieces
of cloth to produce a desired end.

To use a metaphor you might be more familiar with, I'll use an example
from my own life: When the World Wide Web first came in to creation,
we all wanted a piece, and vanity pages became all the rage. While
some folks probably learned HTML code in a class, the vast majority of
us (myself included) learned HTML by viewing the source code of a
website and tinkering it to create different effects. There were
certain rules we had to follow or the whole thing would break, but
once you learned those basics (close your tags!) you could impress
your own aesthetic control over the output.

So to utilize this metaphor, imagine that an item of clothing is a
website (Old school, HTML-based. I've yet to grasp CSS so I'm not even
going to touch that.) and that certain tags control certain results.
If you look at the "source code" by either taking apart a shirt or
analyzing it's different parts, you can replicate it using the same
rules, and tinker with the aesthetic output. Take out your favorite
shirt and lay it flat. Flip the collar up and look at what that
pattern piece looks like flat. Kinda different from what it looks like
while worn, yeah? Now if you're trying to replicate it you can play
with the height of the piece, or the edge treatment, or the points,
but it's still going to behave a lot like the first collar once you
put it on the body. It's actually going to be harder to completely
"break" the second collar than it would be to break a web page.

And THAT is actually making it even more complicated than it needs to
be. You can start with absolutely no basic model and cut out pieces of
fabric, tweaking and draping (yes, that's a technical clothing design
term) each piece on to the body, pinning it all together, until you
get the shape you want. No special tools or knowledge required.

Patternmaking and clothing assembly is a very intuitive craft, because
it doesn't need to be more complicated. Getting our brains and hands
to wrap a two dimensional object around a three dimensional one is
SUPER EASY, and in fact way, way easier than the amount of programming
it takes to get a computer to do the same task.

Does the software to do this exist? Sure. I have some called
PatternMaster that's pretty nice. And really expensive. And doesn't
run on a Mac so I haven't used it in a while. I'm about 100 times more
likely to just bust out a piece of fabric and start hanging it on my
body until I get it to be the shape I want.

Some basic geometry can help, sure. If you really look at a pair of
pants it's really just two tubes that have been connected and had the
crotch excess removed. A pull-over shirt is one big tube with two
smaller tubes attached. A dress is a long version of that. A skirt is
a tube squinched in at the top. You can start with these tubes and
shape them by creating darts or additional seams, and with enough
tweaking it will wind up looking like clothing. I guarantee it.

Unfortunately the last 200 years of mass-production has created a
population that has ceased to use their brains in this way, because if
you're just busting these tools out for the first time it's going to
take you a while to learn how to use them and some people see this as
a monumental obstacle. But they're there, I promise.

We've already got the tools, we just need to get over the fear of using them.

In terms of tools for that kind of work, Blender 3D and Google Sketchup are both free 3D programs, and Sketchup has a plugin for unwrapping a model (for papercraft). Don't know if it would be entirely realistic for doing clothing designs though, since it works with polygons. Blender offers polys or NURBS, which would probably be a better choice as it consists of building a 3D model out of large planes rather than small squares (more like sheets of cloth). I don't know if there's anything yet which could export that, but I wouldn't be surprised if there was a way to do it