I use Let's Encrypt to provide HTTPS on VirtualGL.org, TurboVNC.org, and
libjpeg-turbo.org, but it doesn't appear that they currently or will
ever support code signing:
https://community.letsencrypt.org/t/do-you-support-code-signing/370/4
Code signing means that the CA is signing off on their trust of an
individual developer, which requires that they perform an identity check
and such. I generally have to find a notary public and send a notarized
affidavit (under penalty of perjury) along with photocopies of documents
that prove my citizenship, current residence, and that I'm doing
business as a developer. It's a colossal pain in the butt.
DRC