Saturday Mac riddles 1

Saturday may not be the right day to plough through a long technical article. You want something a bit lighter, more succinct, and different.

Here are a couple of riddles related to Macs and computing: can you work out what they refer to?

I’m supposedly cheap, but invariably more costly.
I’m one, and I’m several.
And after all that I do for you, you tell me I’m not required after all.

I came unexpectedly one day, intended for the scholars among you.
Those who found me saw me among their most secret things.
I may have gone now, but you can be sure that one day I’ll be back, particularly if you join my class.

Finally, for those who enjoy mathematical riddles, which two (different) numbers are half of each other?

I will post the answers here on Monday morning, when you can try to convince me that your alternatives are more appropriate.