Hmm found this over at Wiibrew so it must be deemed legitamate for Homebrew usage:
Dop-IOS lets you download and install any IOS from Nintendo servers. You can also apply the trucha bug to them.
Features
Download any IOS from Nintendo servers
Select between oldest version or newest version of any IOS
You can apply the signature hash check (trucha) again
You can also apply ES_Identify function patch to IOS36 (useful for AnyTitle Deleter and >3.4 users)
Protection: you cannot install stubs. You could get a brick if you install an stub IOS that your System Menu uses. If you want them, just update through Wii menu or disc.
Stores files on SD: you can reuse all your downloaded IOS with Dop-IOS or another application.
Shows your IOS versions
Why?
Dop-IOS started as a simple modification of Tona's Shop Installer. I wanted to trucha patch my IOS36 in order to play my Super Smash Bros. Brawl texture modifications on 4.0. I could install an older version of IOS36, but then my original games like Pikmin 2 or Punch-Out always asked me to update. These games include 3.4 update with all bugfixed IOS. So the only way to get trucha games on 3.4/4.0 without being asked to update by newest games was to download latest IOS36, patch and install it.
If you are on 3.4 'dop' IOS50, if you are on 4.0 'dop' IOS60. Then you will be able to load trucha games on System Menu (with a modchip, of course). Now you must 'dop' other IOS:
IOS36 (for Smash Bros. Brawl and other Nintendo games)
IOS21 (for third-party games like No More Heroes or Dragon Ball Z Tenkaichi 3)
Some games could use another IOS. You only need to know which IOS they use and 'dop' it.
Brick risk?
Yes. Any application that modifies NAND can brick your console.
Be careful when you are going to 'dop' the IOS that your System Menu uses. A power cut during installation can brick your Wii.
Also, don't try to 'dop' IOS60 if you are using Preloader, because you can get a brick.
History
Version 4
It seems that ES_Identify patch can be buggy in other IOS than 36. So now Dop-IOS is able to apply this patch only on IOS36.
SD files now are stored on sd:/00000001 and they can be used in other applications.
Now Dop-IOS v4 shows your installed IOS versions!