xslide is a major mode for (X)Emacs for editing XSL Stylesheets. Its features include an XSL customization group for setting some variables; an initial stylesheet which is inserted into empty XSL buffers; a "template" menu for jumping to template rules, named templates, key declarations, and attribute-set declarations in the buffer; an "xsl-process" function that runs an XSL processor and collects the output; syntax highlighting; an "xsl-complete" function for inserting element and attribute names; an "xsl-insert-tag" function for inserting matching start- and end-tags; automatic completion of end-tags; automatic indenting of elements with user-definable indentation step; and a comprehensive abbreviations table.
gmuck assists you in generating valid (X)HTML by examining the source code that generates it. It is not a replacement for real validation tools, but is handy for quick checks and in situations where validation of the actual markup is troublesome. It is a line-oriented tool, so its structural checking capabilities are limited, but it makes an attempt to report syntactical errors as well as providing some lint-like features.
Portecle is a GUI version of the command-line keytool provided with the Java SDK. Portecle can create many different types of keystores, generate and store keys and their associated X.509 certificates, generate CSRs, import and store trusted certificates, and perform maintenance on keystore entries.