Sometimes it's the small things that impact conversions most. Here's a small announcement from Twitter that could be a big help to companies like HotelTonight and American Express that are pushing app downloads and trying to spread mobile-only discounts,
Yesterday Twitter announced that, as of now,

...users will be able to tap a link to either view content directly in your app, or download your app, depending on whether or not they have your app installed.
This function works for iOS or Android devices.
Foursquare has already adopted the technology.
For a travel company, what does the news mean? Here's the view of analyst Erick Schonfeld:

With download links, every time someone shares something on Twitter via a mobile app that implements these types of cards, all of their followers are just a click away from downloading the app—every time they share something.
That is huge. The more people share from a particular app on Twitter, the more that app will be downloaded
Here are the two scenarios:
If a potential customer has already downloaded your app
As a travel brand, you can now publish a tweet that, when clicked, directs a user to you mobile app and where they are already signed in with their payment credentials stored.
That seamless connection will likely mean a higher rate of completed transactions compared with sending customers to, say, a mobile-optimized web page where the user isn't signed in and doesn't have their payment details a click away.
An offer for a mobile-only rate on a local hotel that you share in a tweet on Twitter can now link to the page in your company's app where the customer can book it.
If a potential customer doesn't yet have your app
The new Twitter function means you can tell your followers about your app and let them click to download it instantly.
Given that activity is moving to mobile devices rapidly, travel companies that act to convert their social media followers into customers who have downloaded their app will have an edge over their competitors.
If your app is free or has a price, that information will be readily transparent.
A company's coders can enable mobile app deep-linking by inserting a set of markup tags, plus approval from Twitter.
Big move for Twitter
Business-wise, the move is significant for the social networking site because, up until now, it has been reluctant to send users of its mobile Twitter app outside of its app.
Many companies may embrace it. AmericanExpress, for instance, has been aggressively cross-promoting through Twitter ("don't tweet without it") such as by offering promotions. After you link your Amex card to your Twitter account, you can start making purchases by putting particular hashtags in your tweets.
The potential for innovation is considerable.