Multi-Networking in Linux - Multiple Subnets

Normal - you connect yer box to "THE Network",
some dot address.

But what if you want it to see MULTIPLE subnets ...
192.168.0.x and 192.168.1.x or more ???

Some routers, with some work, can do this - but
I've never got it to work cleanly. Didn't need
to so I didn't put in a huge amount of time.

What if you DON'T wanna use a router, just want
the other subnets to be "out there" and reachable ?

I've seen some theoretics, but never any
really solid formula. Never tried any.

Has anybody made this work ? The adapter
must not see just ONE subnet, but a LIST
of subnets and translate one to another
seamlessly.