The bulk of the work may reside in converting custom modules from NSAPI to the Apache API.
Nearly all the other server side technologies (Java, Perl, CGIs) should be portable with little
or no change.
Netscape is tightly integrated with LDAP servers. You may be also interested in LDAP modules in
http://modules.apache.org.
Netscape includes server side JavaScript support, you can check the Apache equivalent,
mod_javascript.