This plugin allows you to easily extend event creation to anonymous users. These users will be required to provide their name, email address and complete the Captcha correctly in order to submit an event for approval.
You need a reCaptcha key for this to work - available from https://www.google.com/recaptcha/admin/create or https://admin.recaptcha.net/recaptcha/createsite/. Place the private and public key values in the plugin parameters.