I came across this project which aimed to reimplement a collaborative text editor (a la Etherpad) in OCaml using Ocsigen. I’m not sure if the author’s here, but we could benefit by looking at the code for learning by example.
Do you know (or have) any other open source Ocsigen projects you would like to share here?
If you are looking for examples, Ocsigen Start is probably the best starting point. It contains an app skeleton for getting you started and plenty of examples for learning Ocsigen .
The Eliom open-source applications that come to mind are the link-sharing site Cumulus and the wiki engine Ocsimore.
There are quite a few open source applications using js_of_ocaml, e.g., Try OCaml, JsCoq, CueKeeper, and a TODO MVC implementation.
Additionally, a look at OPAM will reveal many libraries and frameworks that use some part of Ocsigen. And of course there are quite a few non-open-source projects. For example, BeSport is an entire social network built with Ocsigen and OCaml technologies.
Logarion is using Oscigen’s TyXML here for HTML composition.
A secondary goal of the project is to provide an example rich code-base, but it’s not there yet by any means.
A while ago I implemented a simple dictionary webapp, using js_of_ocaml and tyxml: http://git.isomorphis.me/dict/about/ . It is completely executed client-side.
In order to discover Ocsigen, I migrated a small java project here. This project is certainly useful above all as an anti-pattern example 
The other interest is that it is very small, which can facilitate his reading.
It implements a REST interface, uses Xmlm to parse open data and uses Ocsipersist for persistence.
Hopefully that may be of interest.