API3's voting app implements a simple quorum-based voting mechanism with:
a minimum required voting power to create a new proposal (defined in the Pool contract)
a minimum required quorum for passing a proposal (after a waiting period)
a quorum percentage to pass a proposal instantly
Proposals include an execution script, which can be executed if the proposal passes.
The API3 DAO has installed two instances of its voting app, primary and secondary versions, along with two Aragon Agents that they control. The primary commands a larger treasury and can update all DAO settings, while the secondary commands a much smaller treasury and can update some of the DAO settings.
See the Api3Voting.sol contract code and the Aragon contracts it inherits from.