What are viable alternatives (FLOSS+Mail+Calender+GUI)? I've used Evolution before and it was pretty good, I guess I'm switching back to that (more importantly

What are viable alternatives (FLOSS+Mail+Calender+GUI)? I've used Evolution before and it was pretty good, I guess I'm switching back to that (more importantly I will have to switch my parents' computers as well, they have happily migrated to Linux). Claws also seems good at first glance. Have heard KMail and Trojita mentioned before but I'm not sure how much overhead having Qt for them would be (so basically ceteris paribus I'd rather have something GTK as Xubuntu is my distro of choice). I guess Exchange integration would be needed eventually but I could work around that if need be. Linux and OS X support preferred, could live with Linux only.