If you soup your own film, you've probably heard of "The Massive Dev Chart
" by now. A vast, "crowdsourced" database of film and developer combinations with development times. An indispensable resource if you really like to mix it up and experiment.
Not all of us have computers in our darkrooms, kitchens or even bathrooms though. What to do? Check out their mobile apps
I picked up the iPhone version of it quite some time ago, and find it indispensable alright. It contains the database and a plethora of tools - perhaps the real gem of the app, the timer.
You can select your favorite combinations of film and developer (and save them for rapid selection later on), along with other timing functions for stop, fix and wash cycles. From the first drop to the last, the timer will visibly and audibly guide you through the entire process, along with proper agitation alerts. There's even a daylight and darkroom mode.
The price has gone up since its initial release, and currently goes for $8.99 via iTunes. In my opinion, it's still worth every penny. I can't recommend this application highly enough.