I use Rollbar for error monitoring and they still have a free tier even when divorced from Heroku. So does Papertrail.

I use Amazon SES for mail-sending because I have issues with all of the Heroku free tier products. I think I might pay a dollar or two for this each month.

Render offers a managed Redis product with a free tier.

I haven't had need for anything else, so ymmv.

These pretty much cover it for me, too. Thank you.

I try to keep such coupling to a minimum, though. Only when the alternative to a `heroku add ..` is really hard, I prefer to have a much more flexible SOME_SAAS_KEY env var and use that in my app/adapters rather than having heroku shoehorn it in. Because the latter only ever ties me further into Heroku.

Which, following YAGNI, may not be an issue today, but does make your agility and ability to react to market changes (such as alternatives being a better option) much less. I try to keep my software platform agnostic because any tight coupling will haunt me in future.