Actually no, .png's are barely used in games as they just use up way too much memory, the most common used are .dds (DR too, open and convert with Ps or paint.net).
Object format is currently Leadwerk's .gmf which is a binary format and as such cannot be decoded. As of this .3ds isn't supported (and probably won't in the future)
Converters are UU3D
(it costs and is a 3rd party tool) or the fbx2gmf.exe converter which comes with the Leadwerks engine (well... I got it from somewhere in the forums of leadwerks.... aaand... I don't know where the link is.... even if I would find it.... I'm not sure if it's even legal as I've not purchased Leadwerks engine, but there was somewhere a link out there to download :/)
Anyways, both are and will not be supported for quite sure, I bet. They are just unusual to use and not really made for games.