Do you catch customers before they leave?

I was wondering how can we better catch customers, before they leave our site, and how can we try to convert them.

Me myself I have:

1. Ecommerce shop - I offer a small percentage sale (coupon code) in exchange for email. And I contact them afterwards if they do not finish the sale.
2. Micro SaaS - offer a cheaper yearly subscription via popup, and again I contact them via email with an offer nobody can reject :).
3. Blog - with popup I offer ebook of an article directly to their email.

What are your good practices to catch customers, do you use some? What do you find useful?

I was thinking also, it might be a good idea to try to make catching customers a small SaaS project. Not sure about the niche, but maybe we can discuss it here.