The Unity developers have been porting their Unity Editor to Linux from Windows / OS X to complement their existing Unity runtime support for Linux.

Porting the Unity Editor to Linux has been a lot more work for the developers than their porting of the Linux runtime support. With the Unity design, most of their real tech is within this game editor/developer and thus it's more complex in porting the C#/C++ code-base to Linux.

Among the issues encountered have dealt with the editor not supporting case-sensitive file-systems, poor handling of compiler macros in the past for Windows/Unity, and making wrong assumptions about compilers and native applications.

Unity developers plan to only officially support 64-bit Ubuntu Linux with their ported effort but it should also run fine on other Linux distributions.

More details via this blog post by Na'Tosha Bard.