I've seen a few users mention that certain SE sites like SharePoint and MathOverflow are unique, as they were originally created as Stack Exchange 1.0 sites.
As a fairly recent user, I don't know what Stack Exchange 1.0 was like. The current version of Stack Exchange is the only version I've ever known.
What was Stack Exchange 1.0? What changed between SE 1.0 and 2.0?
In terms of the software itself, absolutely nothing. It's an arbitrary name that was invented to refer to the old sites which used the paid software provided to them, most of which were integrated into our network again at some point.
"Stack Exchange 2.0" was another arbitrary term used to highlight a huge turning point in the network. We stopped providing the software in exchange for payment and started using the Area 51 process to create new sites instead. You can read more about it in the blog announcing the changes.
Using version numbers here was a "just because nothing better came to mind" kind of decision. The software itself is versioned in the sense that we have revisions of when changes were made, but there's no definitive "these features all make up version 1.0" because features are integrated as they are developed. The software has changed a lot of the years and even what the site looked like just after the "change to 2.0" is vastly different than the still-current 2.0 label.
So don't think of them as anything more than arbitrary, meaningless numbers. A better term for a Stack Exchange 1.0 site is a Pre-Area 51 Site.
