OT Which are the most important websites for site managers

Hello,
Could someone tell me, which are the most important websites for architecture, building construction, engeneering in english?
I come from Germany, where the websites like baunetz.de, bauen.de, bauen.com and bau.de are very good. Now I'm looking for something else in the english speaking area. A website for practitioners, like site managers.
Can you help me? Thanks!
Maria
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