Available for iOS and Android in both free (ad sponsored) and pay (no ads) versions, this
is the best medication app I have found. It is capable of setting reminders for even semi-complex medication schedules (eg, take one pill on day 1, two on day 2 in the morning and one on day 2 in the evening, then one pill on day 3). There is a notes feature which records date and time-stamped notes. I've been using this feature to record side effects and symptoms. The app is able to export the information in a variety of formats. Medications can also be logged on an as-needed basis (great for making sure I'm not taking too much Tylenol). Additional features include inventory tracking (highlighting a medication when you are running low) and the ability to create multiple profiles - so I can track my cat's medications too.
From ASCO, this app is available for iOS and Android. The medication tool is pretty much useless. In fact the only tool that I found remotely helpful is the symptom tracker. While the app can export your info, it is only able to do so as text in an email.
Available for iOS, Android, and Blackberry, this app provides concise information on all drugs that are available in the US, including side effects, dosages, and alternative medications. The most helpful feature of this app is the drug interaction checker. Enter all of the medications that you currently take and the app will flag which ones have interaction warnings.
From CancerCare Ontario, this app is available for iOS, Android, and Windows Phone 7. It provides access to the patient and physician information sheets on common drugs and chemo protocols used in Ontario. Note that this information is also available on their website.
iChemoDiary, available for iOS only and only in the US iTunes Store, combines treatment and side effect tracking. The app has a nice graphing feature which gives you a visual for when certain side effects occurs in your chemo cycle. Unfortunately the list of available side effects to choose from is limited and cannot be added to. That said, this app would be handy to use during traditional chemotherapy - and it's free.
Another app that has gotten good reviews is called iCANcer. There is no free or trial version of this app, so I haven't tried it. If you are using this app, please leave a comment with your impressions of it.