Here's another of Jeff Minter's golden oldies. Unlike Hover Bover, this one belongs to the blast-'em-out-of-the-universe-before-they-blast-you breed, that is the hallmark of a Minter game.
The screen is filled with a fine mesh grid along the bottom seven lines of which your craft (the Gridrunner of the title) may move freely.
The main idea is to fire up the grid, destroying anything that moves and anything that doesn't until you've cleared the area. Fortunately, your plasma cannon has a repeat fire facility - and you'll need it.
Public enemy number one, and traversing the grid from the top at a rate of knots, are the Gridsearch Squads. These are segmented caterpillar-like droids which, on reaching one side of the grid, drop down a line and zoom back along it. They come in assorted lengths and if the leading segment is hit, the squad is reduced by one but keeps on trucking. If any segment other than the front one is blasted, it splits into two independent squads at the point of impact.
In each case, any destroyed segment immediately turns into a pod. These lodge in the nodes of the grid and gradually change shape. When the metamorphosis is complete, they drop a bolt of energy down the grid which are fatal to your craft - a single hit will slow a pod's growth while repeated hits will destroy it.
Pods can be generated another way. Running along the X and Y axes of the grid are the Zappers. These cheerful little aliens periodically stop and hurl a plasma beam along the grid. When the two beams meet, a new pod is formed. While the Y Zapper's beam is harmful to Gridrunner's health, the X beam is lethal - both should be avoided. When you've cleared the first grid there are another 30 to follow, each nastier and meaner than the last.
Gridrunner is a classic, a rip-roaring, noisy, mad-actioned shoot-'em-up. They don't come any more frantic than this - go get it and get gridrunning.