What's the difference between "in order that" and "in order to"?

In order may be followed either by an infinitive clause,
which is introduced by the infinitive complementizer (for...)to,
or by a tensed clause, which is introduced by the complementizer that.

• He left early in order for Mary to make the presentation.
• He left early in order to make the presentation.
• He left early in order that there would be enough light to drive.
• He left early in order that we would be free to follow him.
• He left early in order that we be free to follow him.

The last example is a fairly rare construction
(called "present subjunctive" by some)
that implies possibility but not necessity.

So that or in order that?

from English Grammar Today

We use so that and in order that to talk about purpose. We often use them with modal verbs (can, would, will, etc.). So that is far more common than in order that, and in order that is more formal:

I’ll go by car so that I can take more luggage.

We left a message with his neighbour so that he would know we’d called.

[on a website]

In order that you can sign the form, please print it out and mail it to this address.

We often leave out that after so in informal situations:

I’ve made some sandwiches so (that) we can have a snack on the way.

When referring to the future, we can use the present simple or will/’ll after so that. We usually use the present simple after in order that to talk about the future:

I’ll post the CD today so that you get it by the weekend. (or … so that you will get it …)

We will send you a reminder in order that you arrive on time for your appointment.(or … so that you arrive on time … or … so that you’ll arrive on time …)

So that (but not in order that) can also mean ‘with the result that’:

The birds return every year around March, so that April is a good time to see them.

According to the BBC:

• In order that you may pass the exam, we recommend you read through all your notes. (Very formal.)

Here's the link:
bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv146.shtml

"In order that" sounds odd to me. On the other hand, I hear "in order for (him to do something)" almost every day. 


According to The Columbia Guide to Standard English:
In American English, it is Standard to follow in order that with may, might, can, would, or any other auxiliary that fits the sense intended: In order that we can have enough time, we ought to leave by noon.


A note about English subjunctive:

In most cases, the Spanish subjunctive for wishes (quiero que, deseo que, necesito que) is expressed in English using "(for) subject infinitive":

I need (for) you to go to the store.
I want (for) him to be happy.

For orders and suggestions, you hear the English subjunctive more:

I mandate/require/ask that you be there at nine o'clock.
(also: I mandate/require/ask you to be there at nine).
I suggest that you be there at nine. (The only way to say it, I think).

"So that" is never followed by subjunctive. 
"So that I am ready..." not "so that I be ready..."