The largest Ruby conference in France: dotRB, October 18

You should also check out the other conferences from the same http://dotconferences.eu series in Paris:

http://dotjs.eu (Coming back in Nov 2013)

http://cloudconf.eu (June 7)

Happy to answer any questions here!

There's also LA-CONF (http://2013.la-conf.org/) in May. It's also in Paris.

There is also Railsberry coming up soon : http://www.railsberry.com/