bradrobertson/apartment — comment on commit 48b7fc29cd0b67a71c52254d4e641658d44b6109
File: apartment.gemspec line 25
By bradrobertson:

It's adding as a development dependency. Which you still need in order to properly develop and test Apartment, but it's not required as a runtime dependency, so people who install the gem to use in their app won't have to use Rails, just ActiveRecord.

This basically came about because I'm using a Sinatra web service to build a public API and I wanted to use apartment, but didn't want to use Rails.