Why?
No, seriously, why?
Browsers are made for this. Why would you want yet another browser with all the stuff that can break with implementing one?
And even if you could integrate a Chrome/Firefox/Opera/Whateverfanciesyourpanties browser in the launcher somehow… WHY?
Same as above ^
And official WIKI would (should) most likely be web based, this because re-inventing the wheel is pointless.
Unless you meant something akin to a text manual, in which case maybe… But a wiki is by far superior to any text based manual and (any decent one) is community driven.
Yet again, why?
Are the applications provided by Discord and Twitch not good enough?
For all the above three suggestions, you can just as easily organize windows in such a way that you have all those features side by side if you really need that.
Or you know, you can tab between them.
The only feature in the lines of Twitch/Discord are probably an in game API that can communicate with those platforms on a basic level. Showing messages and such as an overlay and possibly responding to said messages without switching to the respective applications.
mklink exists on Windows 7, 8 and 10. These are for all intents and purposes identical to symlinks.
IMHO, any in-game documentation should be short and sweet. Pretty much like GT does it right now.
However, a keybind/feature that takes you to the respective wiki page for the item/machine in question in the default browser would be neat.