Possible there is support for Windows and IIS, but their own website strongly suggests otherwise.
EDIT: if they consider their client and their CA as two different products, well, right now the website conflates the two badly. And there's absolutely nothing there to suggest it supports Windows/IIS.
> And there's absolutely nothing there to suggest it supports Windows/IIS.
Their "system" is an API for issuing certificates. There's nothing platform specific about that.
> right now the website conflates the two badly.
From https://letsencrypt.org/getting-started/: You’re welcome to use any compatible client, but we only provide instructions for using the client that we provide.
Edit: This is the protocol they use: https://github.com/letsencrypt/acme-spec
I found the link here: https://letsencrypt.org/how-it-works/
Now I'm just confused.
But I still say: if their mission is to make it as easy as possible to install a SSL cert on any website, as long as they don't have any (apparent) support for Windows/IIS, they're a long, long, long way away from fulfilling that mission and probably shouldn't be leaving beta.