If you’re a mobile developer, this is the one post you need to read today

Couldn't you have gone with a less link-baity title?

Agreed the title is too link-baity for my liking too. I should have probably edited that to something more appropriate before posting.

The post itself (billed as "the one you need to read today") was exceedingly thin and mostly gobbledygook but there you go. A link to http://knappsack.com/ is worth attention.

If it gets around the problems of sharing iOS apps while under development then I am keen. (thinking about it some Android devices can be tricky to get dev code onto as well).

The idea is Knappsack enables a "private app store" for your mobile app development shop, or enterprise. Great for beta testing before launching an app public. Besides mobile, this can be used to distribute Mac or Windows apps also.

This looks pretty awesome, especially given the freemium option for initial testing.

how is this different from testflight?

The major difference is Knappsack is not limited to beta testing and is not limited to mobile apps. Knappsack supports those use cases well but it also works great for controlled distribution of production apps.