Gridrunner was originally a Llamasoft success from Jeff Minter, and has now been Dragonised by Salamander - a regular Noah's Ark of combinations.
Your ship patrols the bottom seven levels of a 27 x 17 grid, the machine code action ensuring speedy diagonal as well as horizontal and vertical joystick movements,
Descending the grid Katerpillar-like are linked Droids, which you can
destroy by hitting the Leader Droid only, otherwise they split into
segments.
You may think the only good Droid is a dead Droid, but unfortunately these mutate into Pods. which have to be shot several times to prevent them descending the screen with a burst of lethal energy.
If all that's not enough, there are also XIY Zappers patrolling the borders and creating more Pods, with the Y Zapper occasionally unleashing a plasma beam which destroys everything in its path (Tactical hint: keep out of its path.)
With 31 different waves of Droids to see off, this game has just about everything you could want and should soon be shooting up the software charts, if it isn't already.