Gridrunner is a fast paced shoot 'em up for the unexpanded VIC-20. The action takes place on a futuristic grid landscape and you take control of a fighter craft at the bottom of the screen. You can move in all four directions with the joystick and the fire button will shoot one laser bullet at a time.

The game itself is clearly based on the old arcade game Centipede. You have a set of alien creatures which start at the top of the screen and proceed in single file steadily down towards you. If you shoot one of the line then the group splits into two and so on. All you have to do is clear the grid of each one of these aliens.

That might sound simple but there are a few hazards waiting to wipe out one of your five lives. Firstly when you shoot one of the aliens it turns into an unmoving spore-like pod on the screen which, as time goes on, starts to mutate through several stages until it reaches its final stage which is to seemingly turn into a missile which heads straight down the screen. If you're below this you will be wiped out. That might sound easy to avoid, but if you have several pods all mutating at the same time you could be set upon by many missiles at once.

Secondly there are two laser guns at the edges of the grid. One is set along the lower side of the grid horizontally and the other is set on the left side of the grid vertically. They will both let off lasers across the grid at random intervals. Again if you're caught in one of these beams or missiles you will lose a life and have to start the level again.

There is a nice side effect to these enemy guns in that they will also accidentally shoot one of the alien creatures which you are attempting also to gun down. But this will obviously create a spore that you need to watch out for. Finally, if the two guns happened to cross fire they will also create a spore.

The action is thick and fast in this game and, as with a lot of Jeff Minter's games, it draws heavily from the look and feel of early arcade machines. It also has some of the best blasting sound effects on the VIC-20 and, as with many games of the era, it just gets faster and harder the further you get.