David Osimo's research results point to three categories that fit the policy cycle: definition, implementation and evaluation.
In the definition phase, crowdsourcing is useful to identify innovative ideas, and filter them. Tools for discussion are probably the mainstream, but the paradigmatic case are idea-storms, like ideascale.com, very much used by the US government. But also wikis, such as the co-definition of the Expertnet project. Or commenting tools like co-ment.com.
In the implementation phase, we refer to collaborative project that actually solve problems, either by identifying innovative solutions such as challenge.gov and simpl.co, or by leveraging distributed action such as criticalcity.org, and the collaborative tagging of cultural content in the Finnish case. These cases use largely social networking technologies, which are very useful in nudging action.
The evaluation phase is probably the most used and popular. In this category I place apps like fixmystreet, for crowdsourcing the feedback over the city, as well as different feedback tools such as patientopinion. But I also place visualisation tools that make sense of open data.