i was using testing the classic library and notice nobody made a version for pico8 ,
the main motive probally is because pico8 uses tokens to limit your scope ,so something like oop can be really token intesive but, i made it anyways so here is classic in pico8.

--classic but in pico8

--class

class={}
class.__index=class

function class:ext()
 local nclass={}
 for k,v in pairs(self) do
  if sub(k,1,1)=="_" and
   sub(k,2,2)=="_" then
   nclass[k]=v
  end
 end
 nclass.super=self
 nclass.__index=nclass
 setmetatable(nclass,self)
 return nclass
end

function class:new()

end

function class:__call(...)
 local obj=setmetatable({},self)
 obj:new(...)
 return obj
end

tip:use with responsibility.

fun! but tokens could be saved (for example condense class.__call__ into one line), and instead of copying all methods into each object, prototype inheritance could be used!