If you're using Windows, you have certainly come across some programs who have some version of the .NET Framework as a requirement.

Over the years, more and more versions of the framework made their appearances, but unfortunately more recent versions have not systematically deprecated the older ones, which leaves us with some mess as to which version of the framework you may need, and which one you can completely leave.
This leads to users having multiple versions of the framework when a single one would be enough ; or missing some versions which they may need.

For example, version 3.5 of the framework is compatible with applications that require the 3.5 (obviously), the 3.0, and even the 2.0, but not the 1.0 !!

So in order to help everyone a bit to know which version may be needed and which one they can completely bypass, here is a summary of those you need :

1.1 SP1 (compatible with the 1.0) : link
3.5 SP1 (compatible with the 2.0 and 3.0) : link
alt link
4.8 (compatible with the 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2) : link

These 3 versions are the only ones you may need. All other intermediary versions can be completely ignored (and uninstalled to save some space as well).

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And now here are a few handy tools.

To check which versions of the framework you currently have, or if your .NET Frameworks are installed correctly, you can use the .NET Setup Verification Tool : link
alt link

To uninstall a version of the framework (if for some reason it has been corrupted or if you need to save some space), you can use the .NET Framework Cleanup Tool : link

To repair a version of the framework in case it got corrupted for some reason, you can use the .NET Framework Repair Tool : link
alt link

All these tools are easy to use and may help you to fix any problem you have with it.
(Notice that these tools have not been updated since 2016 so they don't handle the 4.8 version of the framework.)

Might be simpler to link to the wikipedia page: https://en.wikipedia.org/wiki/.NET_Framework_version_history

Some points to note:

.NET 1.1 has been superceded since 2005, if you're still installing a .NET 1.1 or 1.0 application then you should seek a newer version - To my knowledge it is no longer a supported version of the framework, and having it installed could be a security vulnerability.

.NET 3.5 has been superceeded since Apr 2010. Some applications still use it, but almost all offer a .NET 4 alternative which you should seek to use. It's actually quite difficult to install .NET 3.5 on later versions of windows, especially if they're in an office network with group policy defaults.

EDIT: .NET 4.x is only really supported at the latest version and v-1, you should let windows update keep it up to date.

Basically, these older versions of .NET are really old versions. It's not a mess, it's standard platform versioning, Java is way "worse" for it. I'm not sure too many people actually need advice on this.

I think the thread is more a follow-on to the other Visual C++ guide from the other day...
https://www.gog.com/forum/general/visual_c_redistributable_mess

...with the main point being a resource for older games (rather than applications) that may not get updated at all (+1 to Pouyou-pouyou for doing this). As a side note, another good resource is sereby.org who package up all this stuff into a single "All In One" runtime / dependency installer.

Thanks, this is really helpful.

No that's actually a good thing and it is made to avoid breaking backward compatibility or needlessly complicated the API with backward stuff.

Rather than having a new version that will keep full backward compatibility with the previous version and that would therefore seriously bloat the code base they made it so different version could coexist together.

If you are only using newer program that require .NET 4.7 then you only need .NET 4.7+ installed; but if you want to use an older program that uses .NET 3.5 or even 1.* then you can but you will need to install the older runtime also.

To know which one you needs it is also easy, it is based on the CLR version : as long as the CLR version is the same then the runtime should be backward compatible for example :

.NET 3.5, 3.0 and 2.0 all uses the CLR 2.0 and therefore 3.5 is backward compatible with 2.0.

while .NET 4.0 and up to now with version 4.8 all uses CLR version 4.0 and therefore you only need the latest version for all of those (don't ask me where CLR 3 is gone though)

Honestly it was a hot mess with version 1.* with tons of version issues but since CLR 2.0 things have gone tremendously better.

Actually - MS do not easily offer any other format. In fact I'm not sure you could obtain others without explicit MS support.