A longish thread: state of play of dynamic geometry/graphing (in maths education from a UK point of view - personal opinons may creep into my attempt to keep this factual).
Among others, @mathstechnology, @MathTechCoach, @ddmeyer @TimBrzezinski might want to add corrections/info!
@Geogebra is free.
Available offline on computers (Windows, MacOs, Linux etc), phones & online in browser.
Multiple versions of app available.
1 Million+ pre-made resources online at http://geogebra.org , varying from 'super high-quality' to 'messy' (limited curation)...
(Geogebra continued) ...any of these resources can be put into their new 'classroom' system (recent release). The 'classes' can include Geogebra 'apps', text questions and multiple choice questions. 'Students' work can be seen all at once live by the teacher...
(Geogebra continued)...
Also notable for:
- powerful commands hidden behind graphical user interface (solveODE anyone?)
- a Computer Algebra System (CAS)
- fully functioning spreadsheet
- intuitive, powerful 3D mode
- scripting (including Javascript) available for advanced use...
(Geogebra continued)...
- probability calculator with great visuals
- autocomplete on typing commands shows new uses
- phone apps have *EXAM MODE* to stop use of other apps/internet during high-stakes situation (also useful in a classroom!)
(Geogebra continued)...
Possible downsides:
- the many versions (classic 5/6, online) might get confusing
- no curation of resources: needs our own quality control (prob. wise anyway!)
(Geogebra continued)...
- the new 'classes' are in early stages, some functionality (e.g. mult. choice only 1 answer allowed) yet to be implemented.
- the powerful functionality can be daunting

Personal comment:
- Classic 5 app is my go-to app to make resources and visuals.
@Desmos is free.
Available on phones, & online in browser.
Multiple versions of app available on browser/phones.
Many resources curated by Desmos on website http://www.desmos.com , many more user-created resources out there, currently only findable with an internet search...
(Desmos continued)...
The classroom activities section is a well-established and (imo) a world-leading example of live-online learning environment, where teachers can work with students 'live' in pedagogically sound ways, linking with Desmos graphing/calculator systems...
(Desmos continued)...
Also notable for:
- clean & friendly interface
- obvious educational ethics & pedagogy underpinning design decisions https://www.desmos.com/equity 
(this is not to say that the others don't do this!)
- powerful stats analysis (some slightly hidden in ~ operator)
(Desmos continued)...
- did I mention the classroom activities?

Possible downsides:
- no inbuilt 3D mode (yet?)
- more powerful commands can be hard to find
- Computation layer (for advanced classroom activities) is hard to learn at first (& documentation is somewhat messy).
(Desmos continued)...
- Somewhat US focussed
- Can't yet seem to copy data *out* from Desmos to another app (e.g. spreadsheet)

Personal comment:
- Desmos classroom activities can be amazing examples of good pedagogy made possible in an online environment. 👏
@autographmaths is now free (thanks to @LaSalleEd).
Works offline on PC, and older MacOS (new version coming though). Soon to be available online in browser https://completemaths.com/autograph 
Resources available (notably from: https://www.tsm-resources.com )
(Autograph continued)...
Autograph has been developed over many years with particular love and care from @douglasbutler1 (among others). @LaSalleEd have recently stepped in to make sure it's accessible to everyone for free. 👏
(Autograph continued)...
Also notable for:
- many years of experience from *actual* teachers have incrementally improved this software
- it may already be installed on your school system
- recent updates include complex numbers
- it had one of the first interactive 3D modes.
(Autograph continued)...
Possible downsides:
- key functionality of *constant controller* (e.g. sliders in Geogebra/Desmos) is disliked by some
- The interface feels/looks dated to some
- No apps for iOS/Android (yet?)
- tied to @LaSalleEd environment (does this matter?)
(Autograph cont).
Personal comment:
- many teachers (inc. me) returned to Autograph over years to use features unavailable elsewhere (e.g. 3D mode, slowplot feature). These *are* now available elsewhere (e.g. on Geogebra) but are an example of Autograph's pedagogical awareness.
@CasioMaths make some of the most widely used handheld calculators in the UK, and have made their emulators free to UK teachers. 👏 https://education.casio.co.uk/emulators 
In this context the Graphical Calculators have at least a claim to be comparable to other dynamic graphing software.
(Casio continued)...
Also notable for:
- You can use them in most UK public examinations
- They contain full graphing and 3D modes
- A class set might be easier to use than booking a computer room?
(Casio continued)...
Possible downsides:
- expensive
- small screen, limited quality (compare to mid-range smartphone running Geogebra/Desmos app)
- arguably anything they can do is done better in free software available online
- entering data is a faff compared to a spreadsheet
(Casio continued)...
Personal comment:
- I think the main reason to use these is because of their use in public exams. I think this is a problem with public exams, rather than an argument *for* handheld calculator use.
SUMMARY:
There's plenty more to add, and I'm happy to hear thoughts from the rest of you, but I've tried to summarise what I can for @Geogebra, @Desmos, @autographmaths and @CasioMaths options.
Remember - my opinions are my own, and do not necessarily reflect anyone else's!
(EDIT - I've notice my summary is not a *summary*. đŸ€·Ah well. Apologies. Just read the rest 😀)
You can follow @SparksMaths.
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