Third Party Tool for Business Directories?

Hello again Rails Community,

I’d like to add a subscription based “Business Services Directory” to
a Rails app so that other businesses can advertise under a “category”.

This site currently uses third party tools in many views to offer
event calenders and for taking polls.

Is there a third-party service (like for calendars or poll questions)
for this paid directory listings/search/sign-up service?

I know I’ve seen outsourced “Knowledge Base” functionality so that one
could include a knowledge base within their site. What I need is
similar in practice but different in content.

Thank you for your time.