The "-soft" in Squaresoft is "software" truncated, many software and game developers use this suffix at the end of their name. In Japan, the company was always known as just Square without the suffix, only the games localized for western release bore the name Squaresoft. When they merged with the company Enix, they changed the company name to Square-Enix and dropped the -soft suffix altogether, even for localized games.

On a side note, the Spirits Within was a great film, and was faithful to the soul of the Final Fantasy series. If you don't understand why, then you simply do not understand what the soul and overwhelming message of the Final Fantasy series is.