I am unfamiliar with Joinme.com or join.me but it appears to be a video conferencing site more than screen sharing. So are you interested in screen sharing or video conferencing? If it is the latter and you are screen sharing with another Mac user you can use Messages (nee iMessage)
. If you can stand the price ($29.99) I have found Screens 4
to be my pick of the litter
for screen sharing. It is smooth, fast, and when controlling a remote computer (Mac, Windows, Linux, Raspberry Pi) everything works as if you were physically connected. I use it from my Mac as well as my iPhone and iPad. You can see the User's Guide here
for a better of idea of how it works and what it does. You can download a free trial here
I have no relationship, pecuniary or otherwise, with Screens 4 or its publisher Endovia other than that of a satisfied customer.