🚀 go-pugleaf

 What level of hardware capability and software complexity you need depends
on the circuit you are doing. For a small, slow design (few hundred gates,
clock speed << gate delay) you could probably get by with a PC setup. You
might even succeed in fooling a pcb layout system, changing layers and
rules to allow you to do an IC layout.

 The designs I work on require workstation hardware just to store the
files. We simulate for function, timing and fault coverage and I have
stimulus files that run to tens of megabytes, 10000+ line netlists, etc.
We face design specs that require we _know_ what the part will do before
we build it, which in turn requires that we have an accurate set of models
for a thoroughly characterized library of components. This is what you 
will be missing without the support of a vendor.

 You may be able to develop your own library, determine your timing
model numbers from spec sheets and find a simulator package which will
give you what you need. This could get you through a digital design of
low to medium complexity. You should be aware, though, that a vendor
who acts as a foundry (netlist in, parts out) only assumes the
responsibility that the part will in fact match the netlist. You
assume the responsibility that your design's timing etc. are correct.
This is why you should get design tools that give you the highest
confidence level. If you are on a tight budget or short schedule, you
probably can't afford to do it twice.

 If you want to do an analog design, you would be well off to get
closer to the vendors. To succeed with an aggressive design you will
need to know the characteristics of the process and devices you have
available. This information is proprietary, the IC makers' stock in
trade. The transistor models and temperature dependence of component
values will be critical to making a design that works as built. You
can lay out a circuit that looks good on the screen and works in 
your PSpice simulations with guessed values but rings like Billy-be-
damned because you had less phase margin than you thought. Once you have
found a vendor who can meet your price and service requirements, you
can probably work the information out of them that you need.