The Coq community has contributed a large ecosystem of formalization works and plugins throughout the years. An index of OPAM packages can be browsed online. Users are encouraged to submit their packages to the index.
The Coq community has also built tools around the Coq system. You can also visit the page dedicated to related tools.
You can interact with other users of Coq through the Coq-club mailing list; the list archives are also a good source of information. There is also a wiki dedicated to Coq: Cocorico!, where you can share your experience with other users.