This sticky lists all currently available 3rd party plugins and behaviors for Construct 2.
Word of warning: the use of those extensions are at your own risks. They provide more features for C2 but can also result in troubles at preview or export.
Nevertheless most of the extensions are tested and supported by their author and work flawless.
Scirra does not offer official support for those extension, it is up to be seen with each author of each addon on that point.
If you find a bug, or have a question, post directly in the plugin/behavior's topic.
How to install plugins and behaviors ?
User Saiyadjin did a big job putting in place in July 2017 this google doc which attempts to add descriptions to add ons and determine if they are up to date or not.
You can check the document or check for yourself directly in the forums' topics.
In February 2018 Tom published the
Addon Exchange service, holding Construct 2 and Construct 3 addons.
Feel free to check this out as ultimately all maintained addons should find their way there.
Plugins 1 2 3 4
Third part tools