"I’ve just met four great startups in the last three days. All four were trying to resegment an “Existing Market” – one where competitors have a profitable business selling to customers who can name the market and can tell you about the features that matter to them. Resegmentation means these startups are trying to lure some of the current or potential customers away from incumbents by either offering a lower cost product or by offering features that appealed to a specific niche or subset of the existing users."

All four were approaching it differently. See the article for insight into what works/doesn't.