Earlier quoted context omitted.
Could someone comment on the main complications on developing something like this for both Mac and Linux? From my point of view, they is so much common ground, comparing to a Mac/Windows support, that I'd strive for an application to cover both! And that's not something that you could always decide after launching the first time, you need to have it in consideration during design...
The non-UI layer can be made 100% portable for sure (although in the GitUp case it's not really since I chose to write it in Obj-C for productivity reasons). The UI layer is absolutely not portable: it's all low-level CoreGraphics code for the rendering, some CoreAnimation, and a ton of AppKit of course. You could have a version written in a cross-platform UI toolkit or Java or what have you, but you could not possib…
I think this could be done in Qt with QML, the most difficult problems would probably be the list that popped up on the right at one point and getting the scrollbars right. When it comes to graphics, animation and custom drawing Qt is very powerful, the issues that do pop up are with native controls.