VCS or 2600
This was my family's (i.e. my kids') first video game. We had about a dozen cartridges for it, including all three "Mario Brothers" games (I believe), as well as "Doctor Mario" (my wife's favourite), "Airwolf" (which I played many times years later, with my son piloting while I was gunner, and vice versa), and our all-time favourite, "Frogger"!
I *really* disliked the "Duck Hunt" game that came with it, because it was obvious that it was not a matter of skill, but a matter of luck.
We eventually picked up a second one at a yard sale as a backup, because the first one became so unreliable.
1040 ST
This was my second home computer (following a long run using the DEC PDT-11 (q.v.).
It was given to me by a guy who in turn was given it as a review sample when he worked for a micro-computer enthusiast magazine, after he was done reviewing it. The manufacturer seemed *unwilling* to take it back.
It came equipped with an external 20MB HDD, and the usual TOS. It also came with the Mark Williams C system, which included not only a C compiler, but a whole UNIX-like environment, from shell down to system calls.
I was able to set up UUPC, a PC port of UUCP. This allowed me to have my own "site" (as they called it then) on Usenet, a precursor of the Internet. My first connection to the outside world was an i86 box called 'zinn', running a free version of UNIX; that site in turn connected to the venerable !decvax, so I had a really good connection. I sent and received Usenet news and mail for a good couple years at the address ...!decvax!zinn!rr!kenn.
After a time, !zinn was replaced by a whole ISP, called MV.COM, the first in New Hampshire, and, in fact, one of the first in the nation. My Atari became part of that domain, as rr.mv.com, and my email address became kenn@rr.mv.com.
I wrote a good many C programs on that computer.
I also continued development of my LISP-based text-adventure world, using an Atari port of XLISP.
And, last but not least, I wrote a program in Turtle Logo that drew quilt patterns.
Mega ST
This was another hand-me-down, from the same source as the 1040 ST. It was more powerful, and had a colour monitor, but I didn't like it as well because it had a built-in fan that was (to my ears) very noisy.
So it has sat in the dark, alone and unloved.
800
Somewhere along the line, I picked up an Atari 800, thinking it would be fun to recapture a youth I never had, programming a small computer in Basic. I never did use it.