Originally from ticket #85117.
In 12.1+ you have the Default Start Page option, which is found under Preferences in the global menu. This is also a profile option (Applications Start Page) that you can set at Site level. That will take you straight into whatever function you specify after logging in, i.e., Org Chart.
Then you can also add Org Chart to the global menus as the Home link so that clicking this takes you back into the function rather than the navigator.