People have heard about sharepoint, some people have heard about exchange…. Not difficult to miss if you consider the marketing engine that is behind it. Microsoft is desperately trying to change its business model now that Linux has become an low-cost alternative for people that are not wanting to pay for something that should be free.
The idea behind sharepoint is to tie people into an eco-system that will generate a future-proof eco-system. It took linux years to become ready for the mass market. Now that it is, Windows is only there for specific needs or for the ignorant. The only way windows will survive in the future, is to make it free for the masses.
Now this takes away a revenue stream for Microsoft. So they positioned a new one. Sharepoint is there to surplant Exchange, and to make people dependent.
Here are a few alternatives that already exist on the market (Article on groupwares).