A phpBB Google reCAPTCHA 2 extension for phpBB (v3.1+)
Current status: Initial release. Seems to be in use by quite a few people, given the number of contributions I've seen. I've been using it on my live (but not terribly busy) board for months.
phpBB anti-spambot plugin extension for Google's "new" reCAPTCHA. The tickybox one.
PHPGPL-2.0