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I have a list of points as you can see in the image below. From this list of points, I want to generate a filtered list of points, which is the envelope. Additionally, calculate the area under the envelope.

rawData = 1.`, 1.`, 0.6666666666666666`, 
 0.9316770186335404`, 0.5`, 0.906832298136646`, 0.5`, 
 0.8757763975155279`, 0.5`, 0.8633540372670807`, 0.5`, 
 0.8509316770186336`, 0.5`, 0.7888198757763976`, 0.5`, 
 0.7142857142857143`, 0.5`, 0.6645962732919255`, 0.5`, 
 0.577639751552795`, 0.3333333333333333`, 
 0.5341614906832298`, 0.3333333333333333`, 
 0.453416149068323`, 0.16666666666666666`, 
 0.36024844720496896`, 0.16666666666666666`, 
 0.2670807453416149`, 0.`, 0.21739130434782608`, 0.`, 
 0.18633540372670807`, 0.`, 0.13664596273291926`, 0.`, 
 0.09937888198757763`, 0.`, 0.062111801242236024`, 0.`, 
 0.055900621118012424`, 0.`, 0.`;

points=1.`,1.`,0.6666666666666666`,0.9316770186335404`,0.5`,0.906832298136646`,0.3333333333333333`,0.5341614906832298`,0.16666666666666666`,0.36024844720496896`,0.`,0.21739130434782608`;

Show[ListPlot[rawData, PlotStyle -> Red], ListLinePlot[points]]
f = Interpolation[points, InterpolationOrder -> 1];
NIntegrate[f[t], t, 0, 1, Method -> "GlobalAdaptive"]

l, u = Transpose[Through[First, Last@#] & /@ GatherBy[SortBy[rawData, Last], First]];
f1, f2 = Interpolation[#, InterpolationOrder -> 1]& /@ l, u
NIntegrate[f2[t] - f1[t], t, 0, 1, Method -> "GlobalAdaptive"]

0.101967

Alternatively,

RegionMeasure@BoundaryDiscretizeGraphics[Polygon[Join[Reverse@l, u]]]

0.101967

ListPlot[rawData, l, u, Joined -> False, True, True, 
 PlotStyle -> Blue, Red, Green, Filling -> 2 -> 3]

If you assume "envelope" means the "shrink wrap" of the points, the answer is:

ConvexHullMesh[rawData]

If you want to get the area under the curve, add a point at 1,0.

myRegion = ConvexHullMesh[rawData];

Get the area:

RegionMeasure[myRegion]

(* 0.757764 *)

Get the coordinates:

MeshCoordinates[myRegion]

(*

1., 1., 0.5, 0.906832, 0., 0.217391, 0., 0.186335, 
 0., 0.136646, 0., 0.0993789, 0., 0.0621118, 0., 0.0559006, 
 0., 0., 1., 0.

*)

Show[HighlightMesh[myRegion, Style[2, Opacity[0.5]]], 
 Graphics[PointSize[0.02], Red, Point[MeshCoordinates[myRegion]]]]

Here another way, using the three-argument version of GroupBy:

a = KeySort[GroupBy[rawData, First -> Last, MinMax]];
lower = Values[a][[All, 1]];
upper = Values[a][[All, 2]];
t = Keys[a];
Show[
 ListLinePlot[Transpose[t, upper], Transpose[t, lower]],
 ListPlot[rawData, PlotStyle -> Red]
 ]

And since these functions are piecewise-linear, we can apply Tai's method directly to obtain the integral exactly:

ω = 0.5 (Join[#, 0.] + Join[0., #]) &@Differences[t];
(upper - lower).ω

0.101967