Kittybot is a bidbot that upvotes with 10 votes a day. Multiple users can bid in a voting period. If only one person bids, they get the entire upvote. If two people bid an equal amount, they share the vote 50/50. The higher the bid, the higher percentage for the upcoming vote batch.
You can use this bot tracker site to see when it is profitable to vote:
https://s3.amazonaws.com/yabapmatt/bottracker/bottracker.html#free