This video, published by prissi in the forum, shows the contribution of the developers since 2006, which is the better part of it’s life as an open source project.
http://www.youtube.com/watch?v=rg_KbgFiBhg
For me it’s quite fascinating to see how the number of constant contributors increased, but also the fluctuation of transient contributors. Both aspects tell the story of a very lively and impressive project.
Please also note that the massive contribution of Hansjoerg Malthaner who started the simutrans project is not visible here, since it dates back to the late 90s (until 2004), however it is still in place as the foundation of simutrans. This is also true for the massive contributions, eg. by prissi before 2006.