After a long search I've finally figured out how to embed Commodore 64 BASIC listings into blog posts.
This isn't a game, just a visual demo showing off some of the C64's capabilities. It's taken from two one-line programs in the 1985 Special Issue of Run magazine, posted by L.F.S. and Glenn Zuch. I've combined them.
The Listing
1 poke53280,6:poke53281,6:?"{yellow}":fori=1to19:?:next
2 a$="{up}{down}{left}{right}":? mid$(a$,rnd(.5)*4+1,1)"*{left}";:fori=1to30:next:?"{reverse on} {left}";:goto2
Okay, a few notes here. First off, the Commodore 64 keyboard had special keys for setting and changing color. These are hard to convey in printed listings, so the convention is to use {} brackets and indicate what keys should be pressed.
{yellow} is a special character on the 8 key accessed by hitting control+8; this turns the following output yellow. {up}{down}{left} and {right} are the cursor keys. You get them by hitting those keys. They move the on-screen cursor, changing where the next character will print. {reverse on} is control+9, and that basically reverses the color of the next printed character; a space will be a full color "block", etc.
Peek and Poke show up as commands in a few different 8-bit BASICs... what they do is let you look at (peek) or change (poke) memory addresses directly. This is different for every computer model, of course, and it isn't obvious what exactly they do without a memory reference chart.
Poke 53280 lets us directly change the color of the "frame" around our graphics window, and 53281 lets us change the color of the background itself.
The ? mid$ line chooses one of the cursor direction codes we have at random, making the asterisk appear to burrow in a random direction each update.
So, a simple program that crams a lot into two lines. The original was line 2; I adapted line 1 (changing the colors) from another one-liner to make the colors pop a bit more.