devise_invitable by scambra

Let devise support multiple emails (authenticatable, confirmable and validatable). Maintained by allenwq on GitHub, where it has earned 79 stars from the community.

A modern modular service object toolkit for Rails, that respects database transactions and adds type checks to returned values. Maintained by DmitryTsepelev on GitHub, where it has earned 80 stars from the community.

The guide to build a Rails app from a to z. Maintained by jp7io on GitHub, where it has earned 75 stars from the community.