From WebOS Internals
webOS Internal Related Tools
Cross-Compiling and Kernels
PDK Related Pages
WebOS Internals PDK WebOS-Internals alternative to Palm's PDK
PDK on Linux Running Palm's official PDK on linux.
SDK Related Tools (Comparison Chart)
Komodo Edit is an easy to use cross platform open source editor. Use along side the webOS Add-on for easier development. Complete Code Completion is also available for Mojo. Wiki Page with Screensots and Install Guide.
Aptana Studio is a standalone version of an Eclipse plugin. Very easy to use. You can install the Aptana WebOS plugin by directing Aptana to check this link. If you do not know how to set this up, please look at official Palm documentation here.