DDG does have official(and unofficial) browser extensions and apps for iOS/Android.
Sure, but there are a large number of instant answers that can and do work offline because they're simple, static tables, or are self-contained—existing only to apply transformations on the input (e.g., cheatsheets, natural language unit conversions, and calculations).
> DDG does have official(and unofficial) browser extensions and apps for iOS/Android
A browser extension that just sends the query the same as it would if you hit their homepage is in the "what's the point?" category, just like mobile sites that nag you to install their app when all it does is show you the same content that is (or could be) on the mobile site itself. The "is a browser extension" is not the interesting part. "Doesn't send data to a third party" and "can operate without being connected to the network" are.
!s is enough to redirect to Startpage. :-)
https://github.com/asciimoo/searx
there are different instances : https://github.com/asciimoo/searx/wiki/Searx-instances
It's been on my list of things that I will almost definitely never take the time to actually work on, but I wished what I had was (A) a browser extension or GNOME extension that incorporates an offline version of all the DuckDuckHack modules, and (B) the same thing in an open source mobile app. (This kind of thing could just as easily live in a command line app, though, and I'd be super happy if a project maintainer incorporated them into something like GNU Units.) I looked into it, especially for (B), but I realized that the DuckDuckHack code depends on Perl.