As decribed on the NetFront Widgets Homepage, we are looking at a subset of the W3C Widgets 1.0 specification.
Device API access is provided via Access' “DirectConnect” feature, an ECMAScript-driven interface and includes: “location using GPS and other positioning methods, access to local content stored in the address book and calendar, sharing of music, pictures and movies made accessible by DLNA (Digital Living Network Alliance) technology”.
For all details please refer to the NetFront Widgets Homepage
There's no real store available. However Access set up a catalog of currently available widgets, also as a mobile version NetFront Mobile Widgets Catalog