Yes there is a free municipal wifi. Not covering the full city, but definitely available in streets, parks, etc.
Be aware that the network is shut down at night around 22:00. Don't a
sk me why, i have no idea.
Of course, a lot of bars, cafés also offer free wifi. You can also check Fon network, free if you are a member.
Have a nice stay in Paris
grospompeurfr