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)

I don't know anything about Blub itself, but I've been in a similar situation where there was something about my job that I think should be fixed, but don't want to burn bridges. Here are a few ideas that may help.


Try to fix the issue. Explain to your boss that you think Blub is a bad decision for the health and growth of the company. Provide specific cases and instances where it's hurting the company (or where some other platform would help the company better). Suggest an alternative that you feel is superior and be ready to back it up with facts (remember - objective data). This will allow you to voice your concerns and gauge how your boss responds and how open he is to different technologies (or, how married he is to Blub). You may also gain some insight into why the company is using Blub and sticking with it. It will also give you a gauge of whether it's worth sticking out through it, if the company has decided to change technologies. (Note - this may depend on your boss. Obviously, this won't work if he's in love with it and thinks it's the future of technology.)
Hold out until you get a job offer. You've dealt with it until now, so find a new job and wait to leave until you get an offer. This gives you an easy out - "I've been offered a position that better suits my career goals" (or some other more neutral line). Granted, this doesn't necessarily help your current company, but it's also not entirely up to you to fix the matter.
Say you want to take your career in a different direction. Explain that you would prefer to work on a different platform and that Blub isn't your cup of tea. This allows you to say something along the lines of "I don't like it," without getting into the religious debate of code languages/platforms. As Paul said in his answer, it keeps the reasons for you leaving close to you and reduces the chance of people taking it personally.
Make it clear that it's not the office environment. Make sure your boss and coworkers know that you enjoyed working with them. Offer to connect with them on LinkedIn if you haven't already. Try to keep in touch with them as part of your professional network.


As for your successor and documentation, simply make sure all the issues/quirks that you know of are documented somewhere, either in the code or in a wiki or some other structured documentation platform. Explain in comments why you did something a certain way and be matter-of-fact about it - "doing it this way because our version of Blub doesn't support Alternative Method X." If your successor is familiar with Blub and doesn't mind it, then they're not going to heed any kind of "stay away!" messages. Someone not familiar with it is probably going to think you're just one of those platform elitists and ignore overt messages, and someone who is familiar with Blub and doesn't like it, or is on the fence, will either already sway to your side after more experience,  wouldn't have applied to the position, or would ignore your "stay away!" messages, anyway.
