TrinityCore is an MMORPG framework that's built using C++, and using a back-end of MySQL for the DB content. Trinity was at one point a merger of MaNGOS with many patches submitted by users, that is no longer the case.
If you would like to build your own TrinityCore private server, you may find my Dockerised build environment useful. You can find it at:
The real question is: TrinityCore vs AzerothCore.
Simply because AzerothCore is basically an improved version of SunwellCore, with also imports from MaNGOS and TrinityCore. There is no other project with active development of the original Sunwellcore.
Now to make a comparison, on one hand AzerothCore inherits from SunwellCore all the gaming features that are indeed preferred by the players, that's why a lot of private servers are considering to migrate to sunwellcore/azerothcore based solutions.
On the other hand, TrinityCore has a longer history and bigger community, even if big part of it is now focused on Legion. That's right. There is a mistake in the original question: the 3.3.5 branch is no longer the default branch of TrinityCore (however, it is still supported and actively developed). Starting from October 2014, TrinityCore announced to switch to 6.x development as main branch (currently supporting 7.x).
Basing on what stated below, my personal answer to the question would be the following:
If you want to set up a server application to do constant active development and implementing all needed features, then go for TrinityCore and use the master branch (which is now Legion).
If you want to setup a server application just to play World of Warcraft without being forced to care much of development because all features are already there and players are just fine with it, then go for AzerothCore.
TrinityCore official website: http://www.trinitycore.org AzerothCore official website: http://www.azerothcore.org
Quoted from u/Yehonalhttps://www.reddit.com/user/Yehonal:
AzerothCore is essentially the sunwell continuation
It doesn't have daily commits because the content is very fixed! ( you can see the status of sunwell realm before they released the sources here: http://www.private-status.com/ )
However we've already fixed a lot of stability issues, various content fixes, syncronized most of db structures with TC, allowed clang compilation, migrated to c++11 removing some ACE dependencies etc.
* Moreover its roadmap is focused on architecture/performances improvements with some nice points such as:
* versioning: to avoid bugs over bugs caused by new features and improvements, AzerothCore uses a standardized versioning workflow that allows you to keep your server stable and working. info: https://github.com/azerothcore/azerothcore-wotlk/wiki/Project-Versioning
* modularization: the AzerothCore is modular and is structured to separate the architecture in layers. This to allow essentially 2 things:
** WorldEngine, the base of AzerothCore, will allow you to create a MMO server that can support any kind of application ( The original, never aimed, purpose of TrinityCore... Mangos etc.. )
** Creation of some new modules ( slang: plugins ) that can extends functionalities without patching any code ( transmorg, lua engine, duel reset etc. ) . more info: https://github.com/azerothcore/azerothcore-wotlk/wiki/The-Modular-Structure
And many other interesting things that you can find here: http://www.azerothcore.org/
It takes the best from TrinityCore, Mangos ( such as db versioning ) and Sunwellcore.