According to a story in the Baltimore Sun, the State of Maryland has created an app which is designed to help drivers decide whether they've had too much to drive. The app does more than simply calclulate your estimated blood alcohol content - there are lots of free resources availabe to do that, including this one that is made available through the National College for DUI defense website.
According the story, the app also let's the potential driver play games that will allow them to estimate response times, as well call friends or a designated driver. I'm not too crazy about the part that allows you to report someone who you think is intoxicated - especially in the hands of drunk person. But nothing is perfect.
The app is available through both the apple and google stores.
While I haven't tried it, I think the "game playing" part of the app will be particularly "sobering". The problem with many drunk people is that they don't think they are drunk. If they actually see just how impaired they are, maybe they will be convinced.
While there appear to parts of the app that are specific to Maryland, the other parts could apply anywhere. So even though you are in Texas it couldn't hurt to download it before you go out to celebrate the holidays. Just don't so much you forget you have it.