The programs part of the Staden package provide an excellent and fully
developed set of DNA sequence assembly, editing, analysis and more.

Some of its features include:
GAP4 - Performs assembly, contig joining, assembly checking, repeat
       search, experiment suggestion, read pair analysis and contig
       editing.
GAP5 - The new development version of Gap4, designed to work with the
       large volumes of data attainable through the newer sequencing
       technologies.
PREGAP4 - Provides a graphical user interface to set up the processing
          required to prepare trace data for assembly or analysis.
SPIN - Compares pairs of sequences in many ways, often presenting its
       results graphically and has a sliding sequence window linked to
       the plots.
TREV - A rapid and flexible viewer and editor for ABI, ALF or SCF
       trace files.

For more information and citing, visit Staden's web page and check the
"References" file in the documentation.