Nokia today introduced the Carbide.c++ family of development tools. There are three editions: Professional - for device developers and high performance application, Developer - offering a new graphical Rapid Application Development for advanced level application developers, and Express - an entry level tool available for download at no cost based on the Eclipse IDE.
Eclipse is available for many operating systems (Windows, Linux, MacOS, etc.), but unfortunately the Symbian development tools (and especially the emulator) are Windows-only. So, the Carbide.c++ tools will not help you write Symbian apps on a Mac.