The more involved games come at a cost but it is usually nominal, a few dollars at the most and you have a unique game to keep the guests entertained. The best board games to be found are usually question and answer games, where the guests partner up and try to answer questions about the couple or each other for points or spaces on the printed out board. Many games are able to be customized so that you can enter specific questions about guests or the expectant parents to print out.
One thing that makes a search like this more difficult is that many sites are either directories or attempting to sell a calendar program. The latter usually have something free to give away, but if they want you to buy a program the one they are giving away is pretty generic. Don't waste time trying to make the free one work if it isn't perfect on the surface. There are other choices that are completely free. You may have to try several options, but if you are patient and persistent you can find a truly free and printable calendar.