Despite Fantom being such a young language, there are many projects for bringing Fantom support to your favorite IDE. Note many of these projects are still in early development.
Netbeans FantomIDE (tcolar)
Eclipse F4 (xored software)
F4 is an Eclipse-based IDE for Fantom which is written mostly in Fantom itself. It can be installed as a set of plugins via Eclipse update site or as a standalone application:
TextMate Bundle (msl)
Fantom bundle for TextMate:
The Fantom distro contains configuration files for many common text editors under "adm/tools" including:
The Fantom distro includes a very basic editor called Flux which provides syntax color coding for Fantom, Java, C#, etc.