Today when I was going to look something up on the excellent X3Wiki.com it had ceased to exist :-(

Fellow gamers, take this as a warning and make offline backups of important help sites like this! Playing X3:TC and X3:AP is that much harder now.

There are official wikis, although they do not have that much content right now.

X3: [url=https://www.egosoft.com:8444/confluence/display/X3WIKI/X3+Wiki+%28English%29+Home]https://www.egosoft.com:8444/confluence/display/X3WIKI/X3+Wiki+%28English%29+Home[/url]
X Rebirth: [url=https://www.egosoft.com:8444/confluence/display/XRWIKI/X+Rebirth+Wiki]https://www.egosoft.com:8444/confluence/display/XRWIKI/X+Rebirth+Wiki[/url]
X4: [url=https://www.egosoft.com:8444/confluence/display/X4WIKI/X4+Wiki+%28English%29+Home]https://www.egosoft.com:8444/confluence/display/X4WIKI/X4+Wiki+%28English%29+Home[/url]

(The bad url formatting is due to GOG's stupid forum software...)

I had one look when I got X3:TC and X3:AP and found it rather empty and then found that excellent one that has been my goto ever since. I guess I could start help filling the one on Egosoft's site up.