I have actually never written a review on Appsumo before but I am going to make the exception here. The question on pretty much every sumoling's mind is whether this is as good as sendfox and can it replace other autoresponders. Ok let me help you out here.
If you've bought sendfox you will realize it is very basic and this is not necessarily a bad thing because it is easy to use. INBOX ISN"T BASIC ....and it is still easy to use.

As for the comparison to mailchimp and other alternatives like active webinar. I have had all of those and I did mention that inbox is not basic so I can tell you for certain that the experience is comparable and in the case of certain popular autoresponders which are a nightmare to understand, inbox just wins hands down.

If you are a serious online business owner, all you need from an autoresponder is delivery efficiency and email which is attractive enough to want to make people read. Not the average text email (I hope you're reading this @teamsendfox).
Inbox over-delivers on their promises and that has got to be enough for five stars