capnp-ocaml is a code generator plugin for the Cap'n Proto serialization framework. Cap'n Proto's distinguishing feature is that there is no explicit parsing/serialization step: the on-the-wire message format is also designed to serve as an efficient in-memory data structure representation.
http://kentonv.github.io/capnproto/

Aside from important bugfixes, this release brings a larger and better-designed I/O support library for moving messages across various types of channels. Performance has also been significantly improved; I've written a blog post about the benchmarking and optimization experience.
http://pelzlpj.github.io/capnp-ocaml/2014/09/02/capnp-ocaml-2.0/

An excerpt from the change log follows.  Enjoy,

Paul


=== Backwards-incompatible changes
* Module `Codecs`: change API to accept the more natural `BytesMessage.Message.t`
  instead of `Bytes.t list`.
* Module `Codecs`: change API to accept a `compression` specifier, instead of using
  separate functions and separate types for compressed and uncompressed streams.
* Module `Message`: `to_storage` now returns a list of (storage, length) pairs.

=== Other changes
* Module `Codecs`: fix incorrect encoding of framing headers (for example,
  as generated by `serialize`).
* Module `Codecs`: fix infinite loop in `PackedStream` decoding.
* Module `Codecs`: reduce serialized message sizes, by omitting unused allocation
  regions from the serialized messages.
* Instantiate `BytesMessage = Message.Make(BytesStorage)`, so the user doesn't always
  need to. (Implementation is furthermore defunctorized for improved performance.)
* New module `IO`: functions for moving message data through various types of I/O
  channels.
* Compiler now says something about files it created.
* Corrected compilation errors when using 4.02 `-safe-string`.
* Significant performance improvements across the board.