You don't have to fire up Xcode or download the Android SDK to build an app for yourself that you can use anywhere. For less complex programs — in my case, a companion app for a board game — you can open your web development IDE of choice and build something that should be more than adequate for your needs (and shareable if required).
The screenshot above is a web app I threw together for an ongoing, fortnightly campaign for Game Workshop's Warhammer Quest. It's essentially a more complicated version of HeroQuest. A reasonably faithful iOS adaptation came out not long ago, but nothing beats sitting around a table with friends and doing your best not to freak out when ambushed by several minotaurs.
As a rule of thumb, our group of board gamers tries to keep the involvement of gadgets to a minimum, but we found that calculating gold and experience was a time-consuming process, breaking up the flow of the game as we moved from room to room. Warhammer Quest, like many retro games, features a lot of reference tables spread across numerous rulebooks. While the individual tasks of keeping track of who killed what, looking up the "value" of said conquests and then doing a bit of maths to figure out the final numbers aren't laborious on their own, together they formed a dull process that could be easily streamlined with technology.
There are a few points to keep in mind. Unless you're willing to write up some server-side code, storing persistent data could be problematic. True, you have local storage available via HTML5, as well as cookies, but these are rather fragile and not ideal for a database-like structure (in my example, monster names and their associated gold values). If writing to the file system is possible, then it's less of an issue, but again this information is not on the server, so others you share the web app with won't have access.
You'll also need some web space to host the page, unless you're able to store the required files on your device. Easy enough with a notebook or Android devices, but not so simple on a non-jailbroken iPhone or iPad. Online hosting is the most robust option, allowing others access to your app.