I'm planning on leaving my current job because we're locked into using Blub, with an enterprise Blub framework and a Blub-level web server, on mediocre shared hosting. My coworkers are friendly and my boss is an average small business owner - I want to leave entirely because of the technical reasons. I feel like being soaked in Blub is bad for my brain and making me a worse programmer.

When I leave, how can I explain this to my boss and coworkers? How can I phrase my complaints about Blub productively? What kind of warning can I and should I leave for my successor in documentation?

(trying to make sure I meet the standards)