I'm a software developer at Clarity and I built the weekly digest email that I'm assuming you are referring to.
I can assure you that we do not spy on you and can't keep track of what you have searched for on Google.
The subject of the email is the first question shown in the email. The questions that we feature are chosen based on some internal factors, mainly popularity.
I'm a developer at Clarity and we use PhoneGap to publish our native iOS application to the App Store.
From experience, wrapping our website in PhoneGap has been a really good way to get a native application that has native features like push notifications for "cheap".
The nature of Clarity itself requires you to be online to use the product: browse and search, request calls, ask questions, etc. For that reason, we never looked at providing offline support. If we can't find an internet connection, we show a very simple alert dialog.
I'm a developer at Clarity and was involved in the development of this feature.
This specific feature was developed in house. We keep event logs around for a log of things and this feature is built on top of that. When you visit a certain page showing interest in an expert, we'll schedule a job to send this email. A few hours later, when the job runs, it verifies a few things against other logs and we send the email if it's a good fit.
These days I would take a good look at Intercom (https://www.intercom.io/) to do this. They recently came out with event tracking (http://insideintercom.io/power-of-behavior-driven-messaging) making this kind of feature a lot easier to build.
At Clarity, we chose to do things a bit differently knowing that we wanted to have an optimal experience for mobile devices. I would say that there's no one framework that specifically allows us to do that and that it's more about the mindset than the frameworks.
With that said, your question was specifically for frameworks, so here's a few. Even though we don't necessarily use all of these at Clarity, we probably should given some of the things that we've learned over time:
* http://getbootstrap.com/ - Great CSS library to build responsive websites.
* To handle the complexity of the client side application, a good MVC framework is in order
** We use http://spinejs.com/ here at Clarity.
** I've also heard a lot of good things about http://emberjs.com/ and http://angularjs.org/
** I find that for smaller projects, http://backbonejs.org/ is a good choice as well.
* One thing that you'll notice on mobile browsers is the delay in click events being triggered. Google has a great article describing the problem: https://developers.google.com/mobile/articles/fast_buttons, and https://github.com/ftlabs/fastclick seems to be a popular implementation to solve this problem.