I will suggest a mixture of following:

1. Crowdfireapp.com (Mobile app)
2. IFTTT.com (Completely Free and THE BEST ONE)
3. Buffer.com (Not much options but helps me post on Google Plus pages that other two does not do very well)

I gained almost 1000 followers in 2 days using these three.

If you want to know more about social media tools that are free, give me a call.