Cassette tapes/Reel-to-Reel tapes.
 

After 10 years of having never seen them I have discovered my accumulation of cassette tapes with my party reel to reel tapes. I would like to get them onto my iMac or her PC thingy. Some would say,"Why worry?" But I have a big party coming up and it would save a lot of work if I could get them on the computer. So, is there a program, preferably free, that I can use to do this? This is only for my own use.

You need to get/buy/borrow something which can play those tapes, and then you can import the audio via any PC's line input socket, using some freebie sound recorder program.

That's the simple way.

If you want top quality then you will need an external audio converter. There are plenty on the market; mostly USB connected.

What IO540 said, except with one caveat....

If you've seriously got a real collection, and are not just using the word "accumulation" to talk about, say, half a dozen cassettes, then I would humbly suggest you save yourself the time and outsource the job to a commercial conversion company.

Unlike you, they will have machines that enable them to multi-task and process multiple tapes at one time.

If you are able, first check them for print through/ghosting. Best to wind them forward then back all the way first.