Cotai Water Jet is one of the ferry services linking Hong Kong to Macau. We have reviewed it here.
The service celebrates its tenth anniversary in November and to celebrate they have some promotions.
First, they are offering one way tickets in their first class for $100. To get these, you need to answer three questions correctly on their Facebook page during the promotion period, on Fridays between 11:30 a.m. and 8:07 p.m.
Secondly, if your birthday is on the tenth of the month, you can purchase round trip tickets in standard class for $100. A maximum of two sets of tickets may be purchased within seven days. Full details are here.