This is probably a slippery slope, since there are questions of this form which are clearly off topic ("I really like package X in emacs. How do I get that in Sublime?"). But I'm wondering if questions on how to get emacs behavior, specifically emacs keybindings, are on topic. For example:
No. Enabling Emacs-like keybindings in Chrome requires expertise about Chrome and not at all about Emacs. It's the same expertise that would be required for enabling Wordstar-like keybindings or vi-like keybindings. This is off-topic here.
Emacs-like keybindings are not what makes Emacs Emacs. If you're using Viper, you're still using Emacs. What makes Emacs what it is is primarily its extensibility through Emacs Lisp, both in the ability to solve a problem by writing code and in the availability of a wide range of packages that do things beyond basic editing capabilities.
This, by the way, also means that editors with Emacs-like keybindings like Jmacs, Jove and Microemacs are off-topic. Having Emacs-like keybindings does not make an editor Emacs.
Case in point: this question — asking about Emacs-like keybindings in a tool for which no Emacs solution works, and the solution for that tool doesn't work in Emacs. This question is entirely unrelated to Emacs expertise, it doesn't belong here.
That's a grey area, but it's something that indeed needs to be decided.
The question about imitating keybinds in chrome sounds ok at first (a lot of people ask for that) but it would probably end up opening a can of worms. Deep down, is it so different from your Sublime example?
If we allow "how to imitate emacs in browser X", why would we forbid "how to imitate emacs in editor Y"?
I guess the former "feels" ok because the vast majority of emacs users also use a browser, while the fraction of us who also use Sublime is much much smaller. Then it becomes a question of: is this first a site about emacs or is it first a site for emacs users?
The first option, a site about emacs, is clean and objective, albeit occasionally harsh. It would involve forbidding such questions.
The second option, a site for users, is very subjective and if we were to choose it, we would need to define where the line is drawn.
I agree with Gille's answer that Emacs-like keybindings in otherwise completely unrelated software is probably off-topic.
But defining Emacs through Emacs Lisp feels excessive to me, as it wouldn't even include the earlier members of the family like GosEmacs or the '76 implementation (not that anybody would still use those but still...). By that definition, only GNU Emacs and derivatives, like XEmacs and SXEmacs, would be on-topic. While things like EdWin, which is/was able to run Gnus (quite impressive really) would be off-topic
I also feel uncomfortable excluding things like zile, mg (and other MicroEmacs derivatives), qemacs, which all have their place in the generalized Emacs ecosystem. Maybe the discriminating factor should be whether the software's primary goal is to be (some kind of) Emacs, or something else.
I think that emacs-like behavior outside of Emacs is absolutely on-topic. As Malabarba summarized, this SE site could be either about a specific piece of software (GNU Emacs/XEmacs/SXEmacs) or about its users. I don't see why someone would like to have emacs-like behavior outside of Emacs unless he es also an Emacs user. As such I consider people seeking advice about emacs-like behavior in "foreign applications" part of the Emacs community.
Take, for instance, browsers: not every Emacs user is satisfied with Emacs' capabilities for browsing the web (including me, I admit). Should we send these people away or should we instead point out that Conkeror, Vimperator or KeySnail might be useful to them?
What about an Emacs user that runs GNU screen regularly? It took me a considerable amount of time to configure Emacs key bindings for screen's copy mode (scrollback buffer) and the many articles on the net were too generic and didn't help me.
I think that in the end these "foreign applications" could be regarded as Emacs extensions (like packages from ELPA): if a question pops up about a package you don't use, you can simply ignore it.
Now if it's just about distinguishing these questions from "core" Emacs questions, I'm fine with that. Maybe an additional tag like "emacs-like-behavior" or "non-emacs" could be used for these questions.
