Dropbox's contextual app download prompts

Dropbox enables users to store files online for easy access and seamless collaborations with others. Users who use Dropbox on multiple devices get more value from the product on account of accessing their files anywhere. They're also more likely to keep using the app in the long run.

Why this is really good UX:

• Dropbox shows users who create an account online and don't have the app installed on their device a context-appropriate modal for getting the most out of Dropbox anywhere.
• Users who don't download the desktop app at the first prompt, get another one once they start exploring the app's sharing options. This new modal uses the context of sharing files to explain to users how downloading the desktop app would benefit them.
• Tailoring messages to a specific context makes the experience feel more personal to users and helps them understand how taking a specific action (in this case, downloading the app) will help them to share and collaborate on files.