Base64 - Encode and decode base 64.
Browser - Open a browser from an application on Windows, Unix, or Macintosh.
CGI Query String Parser - Libraries to to parse the query data supplied by HTTP GET or POST requests.
Circular Buffers - Implements the circular buffer producer/consumer model for bytes.
Concatenation Streams - Combine multiple streams of incoming data to create a single stream.
Comma Separated Values (CSV) - Libraries to read and write files in Comma Separated Value (CSV) format. (Excel CSV Format also available)
File Helper - Methods for manipulating files.
Iterators and Enumerations - Convert between Iterators and Enumerations or convert arrays to Iterators or Enumerations.
Line Ends - Converts text files between various system formats.
MD5 Sums - Classes for generating MD5 checksums on String, Byte arrays, Streams, or Files.
NoClose Streams - Create streams that cannot be closed with the regular close() mechanism.
Parallelizer - Runs multiple jobs in parallel, n threads at a time, and waits until all threads are complete before continuing.
Password Dialog - A password dialog box written for Swing.
Random Password Generator - Generate a random String using a cryptographically secure random number generator.
Significant Figures - Handles parsing, rounding, and displaying numbers for scientific applications.
Size Limit Input Stream - Create a sub-stream of a specified length from an existing input stream.
String Helper - Methods for formatting, manipulating, and querying Strings.
String Tokenizer - A StringTokenizer replacement with enhancements.
Straight Stream Reader - An input stream reader that does no character class translation.
Tabs - Tab adjuster that can convert tabs to spaces and vice versa.
Uber Properties - A replacement for the java.utils.Properties class with enhancements.

Modifications

Several tools are useful if you want to modify and recompile these utilities:

Java SDK - Includes the Java compiler.
Apache Ant - for building distribution files.
JFlex - to generate lexers used by several utilities.
Better Template Engine - To compile the website documentation.
com.Ostermiller.Syntax package - To color the HTML source code.
Make - (optional in addition to ant) to automate the build. Consider "make", "make install", "make clean", "make build", and "make javadoc".
CVS - to check out the latest version of these utilities from the Giant Java Tree.
Cygwin - to get Unix utilities (including make and CVS) for Windows.