There are lots of places the progressive enhancement mindset can be put into practice. Of course you do often control the server, so a particular feature being unavailable isn’t usually an issue, but good open source software looks for alternative tools—ImageMagick vs. GD, for example—and adjusts it’s program accordingly.
Dispatches From The Internets
Progressive Enhancement only a client side thing? No!
Turner & Google Vets Create New Content Technology

Some semi-locals (ATL is only 2 hours from Chatty) look to be taking on the likes of ReadSpeaker (who I’ve worked with on Web Standards Sherpa) in the automated HTML-to-spoken-word automation space. If SpeakPage can pull it off, this has some real potential.
Photo upload and progressive enhancement for FixMyStreet

An excellent overview of progressively enhancing image uploads in what many would call a “web app”. See also this great writeup they did on their progressively enhanced maps.
Does SVG text pass WCAG 1.4.5 (Images of Text)?

Léonie Watson investigates and says… yes.
There’s a free template for that.

An excellent piece from Laura Patti, pondering the value of design in the age of so many “good enough” templates and frameworks.
Automatic Testing of BBC Accessibility Standards
A tool for automated testing of a list of URLs for accessibility compliance.
When Touch-Screen Inaccessibility Becomes A Question Of Safety

Touchscreen without audio cues are a big problem, especially on airplanes.
Taking Let’s Encrypt for a Spin

I walked you through my journey to HTTPS a few weeks back, but I’m intrigued by Let’s Encrypt. Honestly, I would have preferred taking that approach as it looks much easier to me.
HTML Accessibility API Mappings 1.0
Ever wonder how HTML should map to Accessibility APIs? Look no further.
WAI-ARIA Graphics Module
This is going to make SVG even more amazing (and accessible)!