We're not going to write a lot on the history of IQ, how the concept developed, etc. There is a plethora of sites out there who will likely do a better job than we could — after all, we'd only be rehashing other people's work anyway.
So we thought it better to just provide you with a few starting points and let you explore by yourself. Maybe one day this will develop into a full-fledged FAQ, but for the time being it's three questions — and not even frequently asked ones.
I hadn't heard of TNS, but knew Mensa. Are there even more?
Whew! You bet!
Many, many years ago a guy named Darryl Miyaguchi created webpage he called A Short (and Bloody) History of the High I.Q. Societies. Although this site hasn't been updated since about the internet was invented, it's still an interesting starting point to find out about the answer to the question.
Yes, without doubt there are (and have been) quite a few HIQ societies. Reading through the Miyaguchi page one cannot help being reminded of the Monty Python "Rock Notes" sketch, but today the picture is a bit clearer. We have created a bit of an overview for your convenience, available as a picture (below) and a PDF.
I know a guy who has an IQ of 170. Does he qualify?
Well, that depends. The number alone doesn't tell you a thing. Simply said, in scientific literature IQ is usually being referred to as how far a person is above (or below) the average. This value is given in "standard deviations" (SD, σ) above (or below) mean. This is somewhat hard to read ("My IQ is 1.666 SD above mean."), so in the past, people have set "mean" to 100 and 1 SD to some arbitrary value (usually either 15, 16, or 24). Using 15 as 1 SD, for example, the above now reads "My IQ is 125, SD15."
But as the "SD 15" part still confuses people it's often discarded - this looks easier, but confuses more. Again, for your convenience and because a picture says more than a thousand words, the explanation is available as a picture (below) and a PDF.
I'm hooked. Where can I read more?
So many books, so little time. And of course we don't know where your interest lies. But there is a small, affordable book out there which is probably a good start. It doesn't cover all aspects in infinite depth - but then, that's impossible anyway. But you could do a lot worse than getting Stuart Ritchie's 2015 book
"Intelligence: All That Matters." (ISBN 978-1444791877)
If you got 26 minutes, there is an interesting interview with Stuart Ritchie about his book on YouTube (audio only).