I do not know of any pair of words that have the same meaning and don't think it very likely (except certain alternate spellings and pronuncations of the same word, where even there it means something, except it is about you: your dialect and background, and there are often pragmatic factors at work). So this sort of question is always a good question, and often one that dictionaries don't help much with.
"OK" is particularly difficult, with many folk etymologies (like letterism for "Orl Korrect") and even an expansion or two (Okey Dokey and okay). It is very informal, and I believe quite universal across brands of English, but perhaps less in Britain. If you believe the Orl Korrect etymology, I think it relates to American Military jargon, presenting on parade. In the computer and mobile world, it has a special role as being short - so OK and NO are the positive/negative answers you can give in two characters. OK often means you are agreeing without really caring one way or the other.
"All right", or "alright", are different spellings of the same thing, and not quite so informal. You can also just say "right". In British English "right you are" is I think the origin of "righty oh" (or various alternative spellings thereof), and is clearly closely related. Alright often means you are agreeing against your better judgement, so is then pronounced in a grudging tone.
Of course both can be pronounced slowly or with strong falling tones to indicate negativity.
Both can be used not to mean "okay" but the opposite (that you have agreed with yourself to make a stand, make a move, or some such)
"Okay, that's enough..."
"Alright, that's enough..."
"Right, that's enough..."
But then there are some slang adjectival uses that tend to be more dialectically limited, and are thus harder to substitute (but people still do at times).
"She's a bit of alright!"
"He's an okay sort of bloke, I guess!"
I could see a subtle difference. I always though the difference was this:
completed - means you've done all the parts of the relevant task
finished - you have done the task as a whole, but you may have skipped some parts.
Example:
I have finished the game, but I'm yet to complete all the side quests.
Edit: Free Dictionary agrees with me
Complete
1. Having all necessary or normal parts, components, or steps; entire: a complete medical history; a complete set of dishes.
Finish
a. To stop (doing an activity or task) after reaching the point at which there is nothing left to do: finished cleaning the room.
b. To bring to a required or desired state: finish an assignment; finish a painting.
Best Answer
Standoffish has more of a negative connotation, the subject being unsocial or even contemptuous (OED), whereas aloof means simply apart or at a distance.
Raymond Chandler uses both words in his personal correspondence:
"I am standoffish with strangers..." (1 Jan 1948)
"What on earth happended between this rather cool, aloof woman and me?" (3 Feb 1958)
An example of aloofian separateness in a poem by Paul Muldoon, "Princess and the Pea":
"Her lying there, extravagant, aloof / Like cream on milk."