Desmos graphing calculator
https://help.desmos.com

UI
   Left text panel.  Top has gear for Edit List (I guess options for each row?).
   Colorful circles are styling buttons.  Single-click to hide/draw; click-hold to configure.
       Can definitely use references to hidden equations.  Only the initial def gets hidden.
   Enable/disable rows by toggling the style button.
      (there are rgb and hsv functions but looks like not applicable to styling).
   Items (rows) are added with + beneath the currently selected row.
   Far left of each row are styling buttons.  To right is Edit List gear button.
   Row options available only in Edit List mode:  convert to table, copy, delete.
   Table header cells have the left style button.
   Can click on "points of interest" in the graph.
   Can move values of points by enabling a drag option in the style menu.
   Can disable zooming and panning with option under 'Graph Settings' wrench.  Also grid and axis.
Basic text entry:
    " to add a notation row
    TAB key to end fractions, superscripts, subscripts
    ± does not work but I think often can approximate with: [-1,1]*
    vars and function names are single letters (incl. greek LC) with optional subdigit.
      x,y,t,r,θ get special behaviors.
        Use any other letters, or add subscripts for a normal var.
        t: get domain limits instead of slider prompt
        x: independent cartesian
        y: dependent cartesian, DEFAULT    Consequently, to get inverse of named fn: x = f(y)
        θ: indendent polar
        r: dependent polar
    "pi" = π
    "sum" = ∑ (summaton operation)
    "theta" = θ (polar independent variable)
    "int" = ∫ (integration operation)
    "sqrt" = √
    e
    (have all the LC greek characters from "words" but can use them as you wish other than π and θ.
    Data tables can also be in text rows.  [I don't know what I meant by this]
Polar:  You MUST use θ as independent and r as dependent vars.  How can define multiple???
Graph ranges
    Canvas (not function) ranges are set under 'Graph Settings' wrench,
     defaults to -10 to 10 x and y.  (Used to have a 'Square Grid' option to lock that, but no more)
     Step range sets how often labels are written on the axes.
    Give equation range constraints, each in a {}
      (this constrains where it's evaluated, not the chart size).
Points
    (3,2)
    As soon as you enter a point spec like above with any variable (that's not defined yet),
      you get options for a slider for each variable;
      EXCEPT for variable t just adds domain limit attributes defaulting to (0≤t≤1).
      Sliders don't need to slide-- can conveniently change the value manually.
      Once you have a slider, click on LHS or RHS limit to domain limits or step.
        Far left to set animation behaviors.
    [Undefined vars in tables are different than in points-- you must define them;
      again x,y,t,r,theta spl.]
    Click on graph to label location
    Multiple:  (1,2), (2,1), (3,0)
    If you name a point by 'p = (1,2)' it gets draggable style.
    If a point definition includes a list then it becomes a list of points.
Equations & functions
    If no [in]equality then it assumes you want: y =
    To re-use a function anywhere, instead of no-equation (previous point) or "y =", use "f() =".
    Can also give "implicit" relations where one side of equation is neither "f()" nor "y".
    Can generate a sample point table with row option Convert-to-Table
    OR define a point list which is just a point def that includes a list.
    After define a function, can define a point on the line for animation and other purposes like:
        (c, f(c))
    Tables.  You can dependent column heading to be exprs. or function calls to auto-gen the values.
    Add table columns by clicking where new heading would be.
    To insert row at top, click on first row and hit ENTER.
Lists: [1,2]  elements.  List of points: [(1,2), (2,4)]
    Can import lists to tables by pasting a CSV or DSV or spreadsheet copy.
    Can use inline like: (0, [1,2,4])
    [0...8] range of ints.  For increment other than 1, give 1st 2 values.
    Can use these as samplings for a variable in your [in]equality or point specification.
    Some functions work with lists, like:  total([2,3])
    Table value entry can hit ENTER to continue adding entries linearly.
Basic keyboard entry
    Fractions Key in:  d/dx TAB  (i.e. TAB ends fractions)
    Superscripts: ^2
    Subscripts digit after a letter
Folders.  Just groupings of rows.  Indicated by vertical gray bars.  Click&drag to manipulate.
    Folder rows can be collapsed/expanded, disabled/enabled
~ Regression = curve-fitting.  E.g.:  y₁ ~ mx₁ + b
    where you have indep. var and at least one dep. defined in a list.
  It generates optimized values for the undefined variables and provides "plot"
  button to add residuals to your table.
Derivatives and Integrals.  d/dx and "int"
Recursive functions.  Just reference the new name on the RHS.
  You'll need to any one ind->dep value pair called "base case".

Special functions.  List them all with the keyboard icon then "functions"
    polygon((-2,2), (2,2), (0,-2))   or   polygon(indVar,depVar).  Can fully style the poly.
    total([list]), mean([list])  and other statistical functions