Still in my opinion, it is the best software I ever found because...
After learning some basics, reading tutorials, you finally try a mission
from Earth to the Iss. You turn off the lights in the room and get ready for
takeoff.
Once in Orbit , after aligning your Orbital plane, after synchronizing
your orbit to rendez-vous with the ISS, setting up communication frequencies...
you see a tiny spec becoming larger and larger.
Suddenly you can make out the solar panels, you realize that you really
are getting there... the Iss
It's at that precise moment that I forgot I was in font of a comptuer
screen in my living room, I was there.
You see it in the Orbiter forums, the joy of those who accomplish a tough
mission for the first time. The veterans give out congratulations and advice
and everybody feels part of a special group.
Orbiter is the brainchild of a mysterious man...
Martin Schweiger, Ph.D.
University College London
Department of Computer Science
On his site Orbiter is described like this:
ORBITER is a free flight simulator that goes beyond the
confines of Earth's atmosphere. Launch the Space Shuttle from Kennedy Space
Center to deploy a satellite, rendezvous with the International Space
Station or take the futuristic Delta-glider for a tour through the solar
system - the choice is yours.
But make no mistake - ORBITER is not a space shooter. The emphasis is firmly
on realism, and the learning curve can be steep. Be prepared to invest some
time and effort to brush up on your orbital mechanics background.
In real life he works on things like "Time-resolved Optical
Absorption and Scattering Tomography" and has made the space simulator
Orbiter for... fun I suppose. With almost 3 million visitors to his site
since 2000 and a buzzing forum, the man has a very active passtime. I asked
him on his forum why did he create Orbiter, here's what he answered...

...there may have been a very good reason for making
orbiter in the first place, but it eludes me now. "For fun" is really the
only thing I can come up with, and even that doesn't really justify the
amount of time I have spent on it. I try not to think too much about it, or
I might decide that I need to get a life
Maybe I can expand at least a little:
Astronomy has always interested me, but I have never pursued it seriously,
other than a few astrophysics courses at university. I thought that writing
an astronomy program of some sort might be a good excuse to re-learn a bit
of mechanics, and at the same time improve my C++ skills.
Since then it has grown beyond anything I had anticipated. The turning point
was probably the introduction of the API which provided a means of getting
other developers on board - lots of them! These days my main interest is in
orbiter as an educational tool, to show that (at least in principle)
teaching and learning science could be fun.
On the whole, orbiter just a hobby that helps me unwind in the evening after
my day job, which happens to be physics and computing - now how sad is that!

As for me I use Orbiter as a teaching tool at the high
school level. Students really love it and I must say that it's the only time
they really make a sustained effort during an experiment. A
software with no score, no sex or violence that students like ?
Makes you think doesn't it.
Orbiter can be quite intimidating because it is so realistic,
but starting slowly you will be very pround of each of your successfull
missions ( after quite a few crashes
)
Contrary to video games, the more you use Orbiter
the more you feel that your understanding of the universe is expanding also.
Thus Orbiter has a lasting effect on it's users.