Outis – S/MIME for Gmail
According to the IETF's outcomes tracking database, S/MIME hasn't been a success. They somewhat charitably say that it has experienced "poor adoption."
For some reason, the heroic efforts of the S/MIME Working Group in creating the dozens of documents that they've finished so far remind me of the part of the Odyssey where Odysseus and his companions escape from the hungry Cyclops Polyphemus by blinding him and running away while his cries that "nobody (ουτις, or outis) was hurting him" were ignored by the other Cyclopes.
Maybe "Outis" is a good code name for the Firefox S/MIME add-on for Gmail. I expect that's who will be using it.