Before I say anything else, I want to very strongly recommend that people abandon abandonware based only on the fact a modern indie game will probably be less hassle to obtain, install and run. You will also only be able to talk to the one other person on the internet who is also playing this game and you don't speak their language.
Not that I'm necessarily a pro-Abandonware person, but the whole point behind abandonware is that you want to experience a particular game, which happens to be abandoned.
Let's say, for the sake of argument, that I want to relive the glories of Stryker's Run, a side-scrolling game for the BBC Micro (of which I have two laying around). I found two examples of this game on eBay, for reference, and Superior Interactive (née Software) appears to be publishing the classic Repton series with plans for Stryker's Run and Codename Droid in the pipeline. So it wouldn't be a legitimate piece of Abandonware (though I don't doubt there's a Warez download/conversion out there). Plus, I've already got my original tape (not that I've run it for a while, so it may not have retained it's playability[1]).
But looking through the rest of my collection, there are a few games that I can't chase down.
"The Magic Sword" (a children's adventure game, I think it used teletext graphic sets in its imagery) has the name and address of the publishers on the cassette-box, and chasing that down I find that by way of at least one company purchase the rights were at one point owned by a computer-games division of a pretty famous household name, but which was in turn was passed onto another company for a pittance due to it not making money. This latest company ignored the educational game market part of their acquisition, so ownership seems to have returned to the family of the man who started the original firm back in the '60s, but liquidated shortly afterwards.
When I search for this game, I can't even find it (to be honest, it's not a definite classic, but the point is that maybe it is to someone), and most references to a game of this name are to an arcade game (later ported to various games console) from the early '90s. So, I'd feel fairly happy (should I have the time and inclination) about this game being Abandonware.
Another game I have that's probably of interest is "Castle Dracula". If you thought "The Magic Sword" was hard to track down, try to separate the wheat from the chaff in a search for
this game name... Its author is a certain "Ray Davies", but almost certainly none of those mentioned (frexample) in the
Wikipedia disambuguation page for that name. I even have an address on the packaging, but checking up on "The Old Piano Factory", NW1, London, shows that I'm not likely to find much trace of the people who, in 1984, sold this game for the frighteningly high price of £7.95.
A text-only adventure, my recollections are that it was fiendishly difficult. Perhaps I could dig up a copy of Zork (or something else now equally open for all to download), but that wouldn't be the same game as either of the ones I've just described. Nor would it be Erik The Viking, for which I might later look to see what that status is, but perhaps first edit the Wikipedia page (apparently the BBC Model B version was "text only", but it wasn't quite... I know for a fact that you pressed a button (Tab?) and the text-only screen was replaced with an illustration-only screen relating to the room you were in, from which you would toggle back).
Anyway, rinse and repeat for any number of other games in this (rather dusty, deserves a better look at) cassette-tape rack that I've just brought down off a high shelf. Not all of them adventure games (I've got Micro Power's version of Chess just here, and they always did tend to go for a lot of stuff very complicatedly programmed at the back-end, giving the player either a challenging AI or a (for the time) good graphical experience for the more mundane platformers/driving games).
As to why I've also got a tape labelled "Emma Abrahams Dance 1989 (Comps)" in it (which appears to have the Romanian National Anthem on it, as well as some tap-dancing tunes, several blues melodies and "Mod Duet Stripper", I have absolutely no idea, but that's nothing much to do with abandonware except that whoever Emma Abrahams was, she appears to have managed to abandon her D90 (?D90?, that's what it says, but surely it's C90) tape case which... on further examination... appears to actually contain a type entitled "KYLIE". Still don't know why it's in my tape-box.
[1] A completely different question of course, is about if one has a legitimate but
unreadable copy of a game's code, then seeks to use of the very same mechanisms being used by others to illegitimately obtain the product in order to 'retain' a valid copy.