Postcron is a tool for scheduling and publishing posts in several Facebook and Twitter accounts simultaneously.

AddThis is a social bookmarking service that can be integrated into a website with the use of a web widget.

Shareaholic is an all-in-one Content Amplification Platform, which includes related content recommendations, social sharing, etc.

Buffer is a software application for the web and mobile, designed to manage accounts in social networks, by providing the means for a user to schedule posts.

Stacker is an easy way to publish & reply on social media.

Postfity is a post scheduling tool for social networks.