+\subsection overview_fondation Basement layer
+
+The basement of the whole toolkit is constituted by the <b>\ref XBT_API
+(eXtended Bundle of Tools)</b>.
+
+It is a portable library providing some grounding features such as \ref
+XBT_log, \ref XBT_error and \ref XBT_config. XBT also encompass the
+following convenient datastructures: \ref XBT_dynar, \ref XBT_fifo, \ref
+XBT_dict, \ref XBT_heap, \ref XBT_set and \ref XBT_swag.
+
+See the \ref XBT_API section for more details.
+
+\subsection overview_kernel Simulation kernel layer
+
+The core functionnalities to simulate a virtual platform are provided by a
+module called <b>\ref SURF_API</b> ("that's historical, my friend"). It is
+very low-level and is not intended to be used as such by end-users. Instead,
+it serve as a basis for the higher level layer.
+
+SURF main features are a fast max-min linear solver and the ability to
+change transparently the model used to describe the platform. This greatly
+eases the comparison of the several models existing in the litterature.
+
+See the \ref SURF_API section for more details.
+
+\subsection overview_envs Programmation environments layer
+
+This simulation kernel is used to build several programmation environments.
+Each of them target a specific audiance and constitute a different paradigm.
+To choose which of them you want to use, you have to think about what you
+want to do and what would be the result of your work.
+
+ - If you want to study a theoritical problem and compare several
+ heuristics, you probably want to try <b>\ref MSG_API</b> (yet another
+ historical name). It was designed exactly to that extend and should allow
+ you to build easily rather realistic multi-agents simulation. Yet,
+ realism is not the main goal of this environment and the most annoying
+ technical issues of real platforms are masked here. Check the \ref
+ MSG_API section for more information.
+
+ - If you want to study the behaviour of a MPI application using emulation
+ technics, you should have a look at the <b>\ref SMPI_API</b> (Simulated
+ MPI) programming environment. Unfortunately, this work is still underway.
+ Check the \ref SMPI_API section for more information.
+
+ - If you want to develop a real distributed application, then you may find
+ <b>\ref GRAS_API</b> (Grid Reality And Simulation) useful. This is an API
+ for the realization of distributed applications.
+ \n\n
+ Moreover, there is two implementations of this API: one on top of the
+ SURF (allowing to develop and test your application within the comfort of
+ the simulator) and another suited for deployment on real platforms
+ (allowing the resulting application to be highly portable and extremely
+ efficient).
+ \n\n
+ Even if you do not plan to run your code for real, you may want to switch
+ to GRAS if you intend to use MSG in a very intensive way (e.g. for
+ simulating a peer-to-peer environment).
+ \n\n
+ See the \ref GRAS_API section for more details.
+
+If your favorite programming environment/model is not there (BSP,
+components, etc.) is not represented in the SimGrid toolkit yet, you may
+consider adding it. You should contact us first, though.
+
+Any question, remark or suggestion are welcome on the
+<a href=https://listes.ens-lyon.fr/wws/info/simgrid2-users>SimGrid users
+mailing list</a>.
+
+<hr>