What about Adam Langley's own Pond protocol, which last I checked replaced OTR with TextSecure's Axolotl ratchet? But I think someone was saying it's quite a nightmare from a UX point of view for now. Any improvements there lately? And couldn't TextSecure be used effectively as e-mail, since it's async, but just put an email-like UI on top of it?
Even Adam Langley doesn't think that large service providers should roll out Pond, presumably because Langley is serious about cryptography and understands that systems like this can take years to iron out and aren't ready for deployment simply because somebody wrote them up.
Axolotl is Trevor Perrin's protocol; it doesn't belong to TextSecure. However: TextSecure procured a pretty significant block of Trevor Perrin's attention to help review and improve their cryptography.
TextSecure is also, as I understand it, significantly older than Pond.
https://pond.imperialviolet.org/