developers and business users can build beautiful custom user interfaces for their Force.com applications that are designed to work perfectly on your desktop and mobile devices.
Visually create apps with drag-and-drop components
Create beautiful, responsive UIs for Salesforce1 Apps
Use custom or off-the-shelf Lightning Components
Important : If this is what you were looking for then please mark it as a "SOLUTION" or You can Click on the "Like" Button if this was beneficial for you.
It's under Setup->Develop->Lightning Components A note I read on the FAQ said it is rolling out now and is only instantly available on new Org's. I created a new Developer org just now and I see it.
Lightning Builder isn't available yet. They covered it in the DF14 Developer Keynote and said it's "coming soon". They did a live demo with the builder tool, but it looks likes it's at least 3-6 months out. For now, only the Developer Console tools to create and edit the various component files is available.
Right now it's in Pilot only. From the Lightning FAQ:
Q: What’s the current release status of Lightning Components framework and Lightning App Builder? A: Lightning Components framework is in Beta. Lightning App Builder is in Pilot.
Important :
If this is what you were looking for then please mark it as a "SOLUTION" or You can Click on the "Like" Button if this was beneficial for you.
A note I read on the FAQ said it is rolling out now and is only instantly available on new Org's. I created a new Developer org just now and I see it.
From the Lightning FAQ:
Q: What’s the current release status of Lightning Components framework and Lightning App Builder?
A: Lightning Components framework is in Beta. Lightning App Builder is in Pilot.
https://developer.salesforce.com/page/Lightning_FAQ