At the current time I have found no implementation of a voting dapp for DAO's. But of course you could make one yourself. As Waalge suggested you could use some multisig functionality to to vote with a group of people.
Another and perhaps better option is to implement a Mixing net, here's a paper about it. In this protocol a per-selected group of parties form a group of mixing nodes. The voting participants can post their vote via encryption anonymously on the blockchain. These mixing nodes than shuffle the votes and decrypt them together. The result is a verifiable anonymous immutable voting system.
The security of the protocol is fully determined by the chosen mixing nodes. Each of the nodes has a piece of the shuffle and if they share/combine that knowledge the anonymity could be broken. Now if every voter is also a mixer node the protocol is completely secure since only if all parties agree to publish their shuffle the anonymity is broken. But note that in this case if a 1000 people vote and all parties need to mix its quite expensive and cumbersome to perform.
That said, both the mixing net and the multisig voting systems are implementations where all voters have exactly the same voting power. One could extend this by allowing some voters to vote multiple times with other signatures.
Hope this helps!