If you're looking for free French apps, you're in luck: there is a wide variety, from dictionaries to learning programs. I've pulled together a list of useful-sounding mobile applications related to French, but please note that I don't have a smartphone or mobile device, so I can't review them or even comment on the quality.
Learn basic French in this app written by and for middle-school students.
A small collection of French books.
Free French Tutor
Interactive study tools.
Find French radio while you're on the go.
Small app to begin learning French vocabulary.
Free app for translating text into French.
French Verbs 650
Learn French verbs and their English translations.
French Word of the Day (Declan Software)
A new word every day, with sound file.
French Word of the Day (Prometoys Limited)
Daily word with translation and sample sentence.
Daily word with pronunciation and translation, plus quiz and option to save
Learn French - French Apps
Four apps for learning a bit of French: alphabet, numbers, gender, and phonemes.
Learn French Quick
French flashcard program.
Learn French with Busuu
Twenty lessons with option to purchase more.
Littré French dictionary
Dictionary of French from the 17th-19th centuries.
Living Language - French for iPad
Eleven free French lessons, with the option to purchase 35 more.
Official app to help you make sense of Paris's métro and bus.
SpeakEasy French Lite
The free version includes 169 French travel phrases.
If you don't have a mobile device, you might be interested in similar online and offline resources:
French verb conjugator
French vocabulary lessons and lists
French word of the day
Pop quiz! Daily French test