This app was mentioned in 1 comment, with an average of 1.00 upvote
You need a pass pass card here for whatever you choose (bike or transport). (4€for the card)
There is a price for people up to 25 years old to use subway, tram and bus in the metropole: Link Depending on how long you stay in lille, you can't take either the monthly (28€), or the year long (23,80€ per month).
The Vlille card is great, but separate from the previous subscription. It's only 36€ (+5€ credits minimum) for a year of using vlille. With that you can take a bike anywhere. If you use the bike more than 30 minutes, you start being charged on your 5€ credit. You rarely need a bike for more than 30 minutes. (PS: if you take both susbcription, Transports & Bike, you only pay 24€ instead of 36 for the vlille).
For the app to see if the stations near you have bike or space available, i recommend Univelo
Cheers