* ran on hardware that I owned (or rented in the cloud)
* had robust de-duplication [1]
* didn't require expensive or proprietary hardware
* ran cross-platform, so libraries can be created, updated, and used on different computers [2]
* uses a web-based UI, so I can see and share my library from any mobile or desktop browser
I'm giving access to the beta in exchange for feedback. I will release another batch of invites when the next release goes live. I've been releasing about every month, but this last version got a case of featuritis[3] and has taken a while to stabilize. If you signed up recently, expect an email next week; sorry for the delay!
If you want to read more: https://photostructure.com/about/introducing-photostructure/
[1] https://photostructure.com/faq/what-do-you-mean-by-dedupe/