LOTS (and thank you for the question ;) )
I guess it all started when I tried to write a LISP interpreter back in the BASIC times, with list cells being stored in DIM'ed arrays. And I always wanted to write a file format analyzer, but never found the time to do it.
From database that one of my projects used I derived a documentation database and a Word macro to create some reference documents, and a couple of ASP pages to display this information. These were mainly project-specific hacks.
Before ASP.Net came along, I developed an XML-based generic list-and-forms framework in ASP. Table information and list and form definitions where stored in XML. The ASP application used XSLT to generate ASP pages containing the data on the fly.
Forms Toolkit was written to search and manipulate Oracle Forms files using the Oracle Forms API.
Recently I try to be less project-specific, and try to share my dev tools: I wrote a utility to check for XHTML compliance, search and extract data from aspx pages (graspx), and a tool to script MSSQL database objects (SMOscript) similar to the sql2000 tool scptxfr.
The latest software I am working on is dbscript, which supports importing and uploading of database scripts, definition of value scripts for TSQL and C#, schema comparison, XML generation. It's sufficient for my needs, but a still work-in-progress for public use.
I describe and document these tools on my blog, downloads are available from my homepage.