Apache Commons Fileupload

http://commons.apache.org/fileupload/ (Apache License 2.0)

Helps handle multipart POSTs for file uploads

App Engine SDK

http://code.google.com/appengine/ (Apache License 2.0)

Allows running code on google infrastructure, through Google App Engine

Diff, Match, Patch

http://code.google.com/p/google-diff-match-patch/ (Apache License 2.0)

Library for finding differences between blocks of text.

Google Collections Library

http://code.google.com/p/google-collections/ (Apache License 2.0)

Utility classes for working with java collections

GWT Image Loader

http://code.google.com/p/gwt-image-loader/ (Apache License 2.0)

Preloads images, allowing size computation and performance enhancements

GWT Maps API

http://code.google.com/p/gwt-google-apis/ (Apache License 2.0)

Enables embedding of Google Maps in GWT pages.

GWT (Google Web Toolkit)

http://code.google.com/webtoolkit/ (Apache License 2.0)

Client side development tools

GXP (Google XML Pages)

http://code.google.com/p/gxp/ (Apache License 2.0)

Templating language for server side html rendering

Joda time

http://joda-time.sourceforge.net/ (Apache License 2.0)

Date/Time library

JTidy

http://jtidy.sourceforge.net/ (W3C License)

HTML parser/checker/cleaner

ROME

https://rome.dev.java.net/ (Apache License 2.0)

RSS feed generator

Apache License 2.0: http://apache.org/licenses/LICENSE-2.0

W3C License: http://opensource.org/licenses/W3C.php