Sidewize is a shoot 'em up released by Firebird in 1987 for the Commodore 64 and ZX Spectrum home computers. It was followed by a sequel, Crosswize.
The four worlds of Omicron, Nu, Delta and Iota are under siege by the Dariard Mutants. The Warriors of the Xeolom Alliance are all that stand between the Mutants and victory.
Source: Wikipedia, "Sidewize", available under the CC-BY-SA License.