Total DOS Collection (TDC) is one collection which attempts to cover Everything DOS-related. While not as user-friendly as eXoDos, it contains a more 'true' experience, including cracks and cheats. The latest release crosses the 500 Gb-mark.
TOSEC is trying to preserve Everything... as in, everything it can get its hands on. Games, books, films, TV shows, etc. And not just the MS-DOS platform, but every platform out there, to such an obscure point that one wonders if those platforms were ever real or not. Some of TOSEC's content is quite esoteric, and some of its collections haven't been updated in years. I honestly don't know how big the complete TOSEC-collection has become, but IIRC it's over a Tb if you add in the PIX-subcollection.
No Intro primarily covers consoles, but also many home computer platforms, including the IBM PC... I think. Currently it only covers three titles. Good to look for if you want something other than MS-DOS.
MAME primarily covers arcade-machines, but has tried its hand at emulating other systems... mostly with little results. A full set of the latest MAME-releases totals over 3 Tb in size, but at least 2/3rds of that can be skipped if you focus on the arcades.
SCUMMVM is trying to build a 'virtal machine' around a few good games and/or companies, instead of providing a huge dump of everything. Ideal for the casuals who just want to get at the biggest hits and such. Last time I checked, it was over 200 Gb in size.
And then there's eXoDOS, which is trying to be a middle-point in all of this, offering a user-friendly interface, as close a 'complete' collection as possible, while keeping itself within its boundaries. It wouldn't surprise me if the upcoming eXoDOS 6 crosses 700 Gb.
Unkillable Cat gave a very good rundown of what your options are concerning collections.
As far as DOSBox and whatnot, DOSBox is a DOS environment emulator. It works quite well nowadays. Rincewind in this thread is a Dev of a DOSBox fork; DOSBox Staging. I think he is probably the best to present what differences his project has, but you can check them
here. The main draw of these forks seem to be to make the emulation better, making unsupported games or features work better or perfectly. There are a bunch of other forks as well, bit staging does seem to be one of the most accepted ones.
Other options include, as Unkillable Cat mentioned, ScummVM. This one has a completely different approach, trying to reimplement the engine of each game they support. This can lead to implementations that are actually very different from the original, although as far as I know most ScummVM games are actually pretty faithful. Furthermore, you can end up with interesting new features, such as the ScummVM version of the Might and Magic game being able to use the mapping system and interface of M&M 4-5. One downside of this approach, of course, is that you only support a limited number of games, since you aren't recreating the DOS environment.
Further on this idea, you also have various engine re-implementations of old games that exist outside of ScummVM (or any other project, for that matter). Well known examples of these include OpenXCom, which enabled a bunch of mods, gzdoom and other Doom engine implementations which many modern wads take for granted, Exult which is a modern implementation of the Ultima 7 engine and Daggerfall Unity. The trend here is that these implementations, being open source and hopefully well documented tend to open up a whole new world of modding to the old games.
Another possibility, though it seems to be very little recommended, is using a virtual machine like Oracle VM to run the dos environment. Although this is not exactly emulation, you will need to work with emulation to get any kind of results, since old dos games depend on direct memory access to interface with devices that no longer are compatible with modern computers such as sound cards. So, for instance, a VM will emulate all the sound card stuff in order to get sound out of the game, otherwise it would be mute or not work at all. Graphics are likewise incompatible with modern systems and windows and need a layer between them and the real hardware. So, since you end up emulating stuff anyway, I suppose DOSBox is the better option.
Yet another option as to running these games is using original hardware. This option, of course, has the capacity to be the most faithful of them all. But you will need a bit of money to get the old computer parts (maybe a lot of money, depending on what you want) and time in order to build the rigs yourself. If you intend to play games from various years, you may need more than one computer to do a decent job of running them, so even space may end up being a factor.
Another interesting option is something like MiSTer, which is a computer that emulates other computers and consoles, but at the hardware level. I don't understand the tech behind it all that well, but what I got from it is that it tries to set different circuits to emulate the circuit specifications of what these computers used. It seems like a really cool idea, but MiSTer itself doesn't have a very good DOS support, and getting it to support older computers is a whole lot of work as you need very detailed specifications for each electronic component of these machines.
There might be other options to running dos games, but I don't know about them. If anyone wants to add to this list, or correct anything wrong I've said, please go ahead!
Another aspect of this all, also bundled in eXoDOS, is the frontend. That is, a quick way of bundling configuration files and maybe game information in an easy to use interface. If you want, you can set up DOSBox in a way that you would your old DOS game collection. Put them in different folders and cd to the one you want to use every time you start the emulator. But some people have done a good job of making visual interfaces that start the game directly. I used to like DBGL because you could set various alternative .exe for each game (so you could run the config program, or some other thing, like the item maker in Master of Magic) and you could put your pdf files for easy consultation of manuals and whatnot.
Older versions of eXoDOS used their own frontend, which maybe wasn't as neat but came pre-made for you, so you wouldn't waste time setting up the entries yourself. It seems the next version is going to use launchbox instead, which seems like a very good system, but I don't have much experience with it. There are also a whole lot other options of frontend, so you can check those out if you want.
(Just don't ask me where to get all of these collections...)
I still miss Pleasure Dome.
Rincewind
Do you know if the eXoDOS guy(s) considered doing something like a virtual file system to deal with patches and whatnot? I've been using something called Mod Organizer to play Morrowind with a ton of mods; and a really nice aspect of it is that each mod is installed in its own unique folder. Once you start the game, the manager calculates which files each mod is supposed to provide (so, if a mod is supposed to overwrite another, the file of the original is still there, but the new one loaded instead) and puts it all in a virtual folder, as if they were all in the mod folder of Morrowind. I imagine something like that could be used so you could have the original version of a game while also allowing (if so the player wants) the use of a patch or a crack.
