As with the Satio, the Vivaz uses vanilla S60 5th Edition, with no Symbian-provided bells and whistles (sadly), but with a custom 'kinetic' front end added by Sony Ericsson. This comprises a Flash-based replacement standby theme, plus a comprehensive (native Symbian) media suite (music, photos, videos).
The Flash-based standby system is fine as far as it goes, but ultimately it's arguably a lot more limited than similar systems in other 2010 smartphones.
S60 5th Edition
Nokia C5-03, Nokia 5250, Nokia 5228, Nokia 5233, Nokia C6-00, Nokia 5230 Nuron, Nokia 5235,
Nokia N97 mini, Nokia X6-00, Nokia 5230, Nokia 5530 XpressMusic, Nokia N97, Nokia 5800 XpressMusic
Nokia C7 Astound, Nokia C6-01, Nokia C7-00, Nokia E7-00, Nokia N8-00