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The web browser created by Apple. Its creation was inspired by the stagnation of other Mac web browsers. Its rendering engine was based on KHTML (which originated in the KDE project for Konqueror) due to that software being tighter and easier to manage than Mozilla's Gecko rendering engine. This rendering engine has come to be known as WebKit and exists as open source. It has been incorporated into numerous projects aside from Safari since then.
WebKit (and thus Safari) places a high emphasis on open standards compliance. This is likely a strategic rather than philosophical move on Apple's part, as Apple must know it cannot use overwhelming marketshare dominance to push proprietary standards, as Microsoft did with Internet Explorer. This move has worked well, and Safari is now one of the most advanced and standards compliant web browsers available.