Geometer's Sketchpad Closed Shop?
2017-05-09 addendum: as of today, it seems not free again. The company website changed.
That's really one chapter of history.
Geometer's Sketchpad was revolutionary in math education, in the 1990s. And, it was very popular. I believe there are also 1 or more Euclidean geometry theorem discovered due to use of such software, but i couldn't find a citation at the moment. But since 2000, many many interactive plane geometry came up. By 2010, it's a dime a dozen, most are free. Most popular is GeoGebra. [see Great Software for Plane Geometry]
Apparently, the company is acquired.
McGraw-Hill Education acquires Key Curriculum
Aug 2, 2012
KEY CURRICULUM: Acquired by McGraw-Hill Education for an undisclosed amount. The Emeryville, CA-based publisher built its brand over the past decades with a series of math texts and materials, along with digital tools like Geometer's Sketchpad and TinkerPlots. But recent years found the print business struggling, leading to a series of layoffs and restructuring to re-focus on its digital offerings. McGraw-Hill, no stranger to dire straits, hopes these tools can jumpstart its own business.
[source: https://www.edsurge.com/news/mcgraw-hill-education-acquires-key-curriculum]
Nicholas Jackiw, who wrote Geometer's Sketchpad, seems now work for SRI International.
Nicholas Jackiw
Senior Research Scientist, Center for Technology in Learning
Nicholas Jackiw is a senior research scientist in SRI International's Center for Technology in Learning, where his interests focus on how digital technologies can uniquely shape mathematical propositions and learners’ intellectual and material interactions with them.
His research focuses on how mathematical ideas are embedded in, and functions of, the cultural practices and representational technologies of the contexts in which they arise; and also on how new technologies and practices imply not just new mathematical representations but fundamentally new mathematical ideas and approaches. That research informs his design and development of new learning experiences, situations, and technologies.
Jackiw is the original designer of The Geometer's Sketchpad, one of the most widely-used, regarded and emulated software tools in education. For 25 years before joining SRI, Jackiw led ongoing Sketchpad research and design at Key Curriculum Press/KCP Technologies, and coordinated Dynamic Geometry implementation projects with institutional partners around the globe.
Well. Go Download at http://www.keycurriculum.com/, and you can use the 80 GSP files at Visual Dictionary of Special Plane Curves. For example, many on this page: Deltoid