Lance,
At our club we have a website, that recognises users viewing platform, so if you log on via your smartphone, you are then able to save as "an app" and converts to a mobile version of the site, this allows us to book, change or cancel tee times, reserve a cart, book other members and guests in, view upcoming events, member directory, etc we then have a separate system to notify all players of their tee time booking 2-5 days in advance depending on the clubs chosen notification period. This can be be useful if friends or opponents have booked you in to confirm tee time, tee and course.
Of course, there is the members home page, that has latest news, local rules, etc and we use facebook and twitter to advise of other bits and pieces.
For all intents and purposes, this appears as an app.