I find AllStays an extremely useful site, with many kinds of travel information including specific information for RV'rs http://www.allstays.com/Campgrounds/campgrounds.htm . It also has an interstate exit guide, giving all the relevant businesses available at each exit listed in sequence. But up until now I at least have only been able to use it on a full-sized computer.
We have made it a practice to always have the "Next Exit" book with us while traveling--really good to know how far it is to the next place to get diesel, find a clean rest room at a Cracker Barrel, find a Wal-mart, etc. To me, once you have this resource, you just don't ever want to travel without it.
Now I have discovered AllStays has their interstate exit information in a form optimized for small smartphone screens. It's a regular website, not an app, and can be found using a smartphone at http://m.allstays.com/ This is very useful to have when traveling, so I thought I'd post it for anyone who has a web-enabled smartphone. The information is free. You can also get to this mobile version from some, but not all, desktops and laptops--it appears to be an Apple vs. Microsoft thing, with Microsoft on the short end of the stick.
The home page on the mobile version of their site also has a finder section for campgrounds and road stores. For those, there is a one-click map, and for the campgrounds there are also one-click links to their websites.