Openstack, as the name suggests, is a stack of open application for building public and private cloud. The project started with joint effort of NASA and Rackspace in July 2010. The project gained support of 3386 people/developer/contributor and 186 enterprises within 2 years of its launch. Some of its corporate supporters include Canonical, RedHat, Intel, HP, Piston Cloud and Nebula. The project code is available under Apache Licence and is hosted on Github.

Components
Like any other Infrastructure as service software Openstack has:

• Compute service code name Nova
• Image service code name Glance
• Authentication service code name Keystone
• Dashboard service code name Horizon
• Object Storage service code name Swift

These are the key components of the project for current stable release code named Essex). All related and detailed information can be found here.

Why it matters to Enterprise?
Openstack is build in open environment and it's know that building a service with contribution from numerous great minds makes more sense and adds dimension to the product compared to closed room with closed source. It uses open source API which makes it widely accepted and more standardized compared to closed API (don't get confused with term Open API or Open Ecosystem, off late everyone started using these term to sell there product in market).

Companies namely Rackspace, HPcloud, Piston, Nebula, Canonical and others are already in the market selling there service and support. Few days back Rackpace announced there private cloud on top of openstack with code name Alamo. Even Red Hat has announced its offering on top of Openstack.

Why it matters to developers?
Openstack project is one of the biggest project written in python and all its codes are available on GitHub, anyone with knowledge of it can contribute after signing the contributor agreement.

Why it matters to jobseekers/college freshers?
With 186 companies (as of now) already participating to build a product on top of the software what more I should say about the opportunity from indeed.

Why it matters to Eucalyptus and CloudStack?
If any of these folks will tell me they are not affected with the Openstack project I will show them this

And this

But at the same time Cloud Computing is a big arena and there is place for everyone so no one is dying but yes there is stiff competition.

Why it matters to Microsoft and Vmware?
Few days back Hyper-V, the MSFT hypervisor, was accepted in the Openstack project and we will have its hypervisor support in upcoming Folsom release of Openstack. I am clueless why their PR never did a press release on the same, keeping a low profile in Openstack project. Ehhh!! Read this.

VMware has recently acquired Nicira which indirectly makes them key contributor to Network as Service project code name Quantum which will be released as core project for upcoming Folsom release. Apart from that Cloud Foundry the PaaS(Platform as service), an opensource project already getting integrated with Openstack with help/partnership from developers at Piston Cloud.

Why it matters to Gartner, Forrester, IDC or Others
These players have new technologies to make money from with their good or bad analysis.

Why it matters to twitterati?
We have got something new to talk about in 140 character and we can prove one another right/wrong or agree/disagree (I am writing this all because of the motivation i got from my twitterati folks, you guys are amazing).