For this week's challenge, I came up with an app named EasyRide which facilitates car-pooling while commuting. You can post new rides, request rides to people travelling to the same or nearby destination as yours.
You can also set a repeating ride so if you are travelling to work everyday in the week, you need not post it everyday. The app will automatically post your ride status and other users can see it and can request to join you.
Another cool feature is that you can invite your friends from your contacts list (not shown in detail) to join you on your ride. Once you click invite, an invite will be sent to your friend and he/she can accept it.