Hi,
What specifically are you looking for? The section you are referring to is essentially an open API used to extend vCenter/vSphere Client functionality. Different things appear there depending on what plugins you have installed on your vCenter and vSphere Client.
When I first installed my vSphere Client there was nothing listed here. I then added the Update Manager plugin. I have also installed the VMware Data Recovery appliance and plugin. This gives me two items under "Solutions and Applications". (Update Manager and VMware Data Recovery)
Cheers,
David