The Apotheosis of VisiCalc
If the name Dan Bricklin means nothing to you, you obviously missed out on the PC revolution's prehistory (or maybe I'm just showing my age). Bricklin is one of the Ur-hackers, author of the almost mythical VisiCalc, the first spreadsheet (yes, there was one: the idea has not been present since the dawn of time).
But more than being a mere coder-god, Bricklin is a man with his heart in the right place. He did not attempt to "patent" the idea of a spreadsheet, and for that deserves our eternal thanks. Continuing this fine tradition of altruism, his latest program goes even further, and is being released under the GNU GPLv2. It's called wikiCalc: it combines the best of Bricklin's past with today's increasingly trendy wikis.
As its home page at Software Garden explains:The wikiCalc program lets you make web pages with more than just paragraphs of prose. It combines the ease of authoring and multi-person editing of a wiki with the familiar visual formatting and calculating metaphor of a spreadsheet. Written in Perl and released under the GPL 2.0 license, it can easily be setup to run on almost any server as a web application or on a personal computer to publish by FTP.
There's also a fuller explanation, as well as the code itself. Whether you do it out of a sense of historical piety, or because you want to play with tomorrow's cool - and open - toys, it's really worth taking a look at.