I don't know if Postcron is good enough. There seems to be some issues from the reviews given online. Buffy seems good, but I'm not sold on it.
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.