OpenSource projects being worked on or completed by various WikiZens:
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RelProject
* Who: DaveVoorhis 
* What: A true relational DBMS that implements TutorialDee.
* Where: http://dbappbuilder.sourceforge.net/Rel.html
** ''See discussion below titled "Nested Rectangle Diagram".''

"Query Tool" (name not formalized) 
* Who: TopMind
* What: A web-based tool that can roughly be described as a cross between ToadTool, MicrosoftAccess, and ExBase for ad-hoc and low-frequency custom reports or querying. Originally I planned it to be an implementation of TopsQueryLanguage, but scrapped that idea because it would have been much more coding. Instead, I'm focusing on an "SQL facilitator" to leverage the power of existing RDBMS SQL (and filling in some of the annoyances) rather than reinvent it all. I've already scratched 2 designs over the years and am hopefully getting closer as I learn from design mistakes that result in too much complexity or confusion. --top
* Where: (No public drafts currently available)

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'''Discussion'''

Regarding "Nested Rectangle Diagram":

''I dig that nested block diagram in the screen-shot. A potentially very nice visual guide. Kudos! -t''

It's actually a relation with nested relation-valued and tuple-valued attributes, though it ''could'' be used as a block diagram.

''Perhaps I'm using the wrong terminology with regard to "block diagram".''

Dunno.  What do ''you'' mean by "block diagram"?

Although it's only lightly nested, here's another similar example: http://www.nytimes.com/interactive/2010/02/01/us/budget.html

''Ah!  Yeah, no, the screenshot doesn't show a block diagram.  It's a nested relation retrieved via a query.''