How to get it?
The best way to get the game these days is to buy it from GOG.com and thus get it free of digital rights management (DRM). Complete Edition of HoMM 3 includes Restoration of Erathia (the original game), Armageddon's Blade (first expansion), and Shadow of Death (last expansion).
At GOG the game is available in English, French, Polish, and Russian. Should you need other languages it is possible to find the game in Finnish, German, Italian, Ukrainian, and maybe some other languages. Send me (Merri) a message at Heroes Community or /r/HoMM Discord if you know of more!
HoMM 3 Remake
VCMI is a re-implementation of Heroes III game engine, but with modding and extensibility built-in! Also multiple platforms are supported: Windows, Linux, Mac and Android. The downside of VCMI is that it is still work-in-progress and depends a lot on available free time of able developers.
Changing the original game is hard as the source code is not available, thus doing more specialized changes requires a very high level of skill which is out of reach for most modders. This is why VCMI exists: to make it possible for more people to do mods that provide more variety than what is possible within the limitations of other fan projects (Era II, HD Mod).
VCMI requires the original game files to function.
Patches for original CD releases
These patches are useful mostly if you're doing research into the game and want to see how it changed over time. For me these were important to find for localization purposes to see what has changed and when. I've collected all official 16 patches into a single 7-zip file for your convenience. Tracking these down one by one is awful!
|Restoration of Erathia version 1.1|
|Patch from 1.0 to 1.1||H310TO11.EXE|
|Restoration of Erathia version 1.2|
|Patch from 1.0 to 1.2||H310TO12.EXE|
|Patch from 1.1 to 1.2||H311TO12.EXE|
|Restoration of Erathia version 1.3|
|Patch from 1.0 to 1.3||H310TO13.EXE|
|Patch from 1.1 to 1.3||H311TO13.EXE|
|Patch from 1.2 to 1.3||H312TO13.EXE|
|Restoration of Erathia version 1.4|
|Patch from 1.0 to 1.4||H310TO14.EXE|
|Patch from 1.1 to 1.4||H311TO14.EXE|
|Patch from 1.2 to 1.4||H312TO14.EXE|
|Patch from 1.3 to 1.4||H313TO14.EXE|
|Armageddon's Blade version 2.1|
|Patch from 2.0 to 2.1||H320TO21.EXE|
|Armageddon's Blade version 2.2|
|Patch from 2.0 to 2.2||H320TO22.EXE|
|Patch from 2.1 to 2.2||H321TO22.EXE|
|Shadow of Death version 3.1|
|Patch from 3.0 to 3.1||H330TO31.EXE|
|Shadow of Death version 3.2|
|Patch from 3.0 to 3.2||H330TO32.EXE|
|Patch from 3.1 to 3.2||H331TO32.EXE|
Download all 16 HoMM 3 patches (28 MB, English only!)