Piwik lets you easily create advanced Custom Segments of Visitors. You can save Custom Segments to reuse them later. As well as being available from the User Interface, Custom Segments can also be applied via the Analytics API. Custom Segments can contain unlimited number of AND and OR clauses, using any combination of more than 40 available dimensions (visitor attributes).
Note: you may also apply custom segments to Custom reports scheduled to be sent by sms text message and/or email reports as HTML or PDF. With Piwik you can scheduled reports on a custom segment of your audience, better analytics for your team members and clients.