Already have implemented

 Editing

• Syntax highlighting
• Error highlighting
• Code folding
• Code formatter
• Comments and "To Do" view support
• Keyword completion
• Method completion using type inference
• Reference resolve
• "add missing import" intention

Execution, Debugging & Compilation

• Debugging support (setting breakpoints, view stack)

• GDK configuration
• Grails configuration
• Run configuration for Groovy scripts
• Make or rebuild java+groovy project entire (Compilation .groovy files to java bytecode)

Grails

• Grails SDK configuration
• Grails controller, view, domain class, job, script,  service, taglib creation
• Grails generators are built in; output to console

Features

• "Go to Class..."  action (CTRL-N)
• Structure View
• Class members view (CTRL+F12)

Coming soon

• "Surround With..." action (CTRL-ALT-T)
• Find Usages action
• Safe Delete refactoring
• Rename Refactoring
• Live Templates support
• Debugging support (evaluate expressions)
• GSP support