This program will produce a stax program that outputs its input.

kolmogorov.stax

Ld_X	store input in X
c"Initial size: `%"P
{
  xx2B
  xVp:SY{{Vpxaz:r-f}M	keep only substrings that leave an unused ascii char after their removal
  |=h#~
  %RD{d	find the length of the longest substring that occurs the most times
    xx_B
    y{{Vpxaz:r-f}M	keep only substrings that leave an unused ascii char after their removal
    |=h#
    ;=
  }hH,d
  xsB
  y{{Vpxaz:r-f}M	keep only substrings that leave an unused ascii char after their removal
  |=h
  xn#vn%v*2-
  2l   	build [excerpt, estimated savings]
  cH0<C	stop looping when estimated savings of best option is < 0
  xnhz:rG
  c'~=HlC
  "Replacing "p nhA].\n:r:}p " with "p c]:}p.  p
  c~]+
  xnh,:rX
  c"Current size: `%"P
Wd
zP'-80*P
L{:Er$mY
c$Gc~*
xs
2l{	build literal
  A]_G:r
  "([```"])""``$1"R
  '"|S
  _A#{_"`1'`GA]:r"+}M
m
z~
Es,s+A+~
c%2>{	are any replacements?
  y%1=
  {	only one replacement
    ,s+A+~
    "1%:r",s+A+~
  }
  {
    yM%3=
    {	all replacements are 2 chars
      y$G-,s+A+~
      "3/F1%:r",s+A+~
    }
    {	general replacements
      ,s+A+~
      ss~~
      "'` /F1%:r",s+A+~
    }
    ?
  }
  ?
}M
,q
'-80*P
A-"Total golfed size: `%"P
}	get next substition char
"etaoinsrhldcumfpgwybvkxjqz"c^+" !',-.:?"+Vp+"`"``\.*+()[^$"-Vp+s-h]