There are a number of work streams within the Ethereum community, all contributing to the buildout of the Ethereum Virtual Machine (EVM).
Both Swarm and Whisper are complementary technologies contributing to the vision of Ethereum as a "world computer". When imagining Ethereum as a metaphor for a shared computer, it should be noted that computation alone is not enough. For a computer to be fully useful, it also needs storage to "remember" things and bandwidth to "communicate" them.
This could be summarised as such:
Contracts: decentralized logic
Swarm: decentralized storage
Whisper: decentralized messaging
In the next posts I will be covering the Swarm and Whisper projects.