Is a gem ready for Rails 4 or 5?

Rails 4: 583 ready, 38 not ready, and 435 unknown
Rails 5: 95 ready, 10 not ready, and 951 unknown

Gems ready for Rails 5

Name Status Rails 4 Notes Rails 4 Status Rails 5 Notes Rails 5 Status or notes updated
oauth2 ready

Standalone gem

ready

since version 1.2.0

over 2 years ago
omniauth ready

-

ready

since version v1.3.1 (https://git.io/vXCd0)

about 2 years ago
paperclip ready

since gem version 3.5.1

ready

since version 5

over 2 years ago
paranoia ready

since version 2.0

ready

from version 2.2.0

almost 2 years ago
pg ready

Does not depend on Rails

ready

Does not depend on Rails

over 2 years ago
premailer-rails ready

since version 1.3.2

ready

since version 1.9.2

over 2 years ago
pronto ready

Does not depend on Rails version.

ready

Does not depend on Rails version.

9 months ago
query_optimizer ready

Minimize query for fetching table row

ready

Minimize query for fetching table row

almost 3 years ago
rack-oauth2 ready

_

ready

since version 1.2.2

over 2 years ago
rails-dom-testing ready

yes

ready

from 2.0.0 https://github.com/rails/rails-dom-testing/releases

about 2 years ago
react_on_rails unknown ready

https://github.com/shakacode/react_on_rails/blob/master/CHANGELOG.md#802---2017-06-04

9 months ago
recurly ready

ready

ready

.

over 1 year ago
redis-rails ready

_

ready

since version 5.0.0, see https://github.com/redis-store/redis-rails/blob/master/CHANGELOG.md#500

9 months ago
rspec-rails ready

apparently full support since gem version 2.14.0 (source)

ready

since version 3.5.0

over 2 years ago
sass-rails ready

_

ready

since gem version 5.0.5

over 2 years ago
scenic ready

-

ready

-

over 2 years ago
seedbank ready

See https://github.com/james2m/seedbank/pull/28

ready

see https://github.com/james2m/seedbank#rails-5x

almost 2 years ago
seed-fu ready

since version 2.3.0

ready

since version 2.3.6

over 2 years ago
select2-rails ready

See Jose's comment

ready

since Harry's comment below

almost 2 years ago
shrine ready

https://github.com/janko-m/shrine/blob/master/CHANGELOG.md

ready

https://github.com/janko-m/shrine/blob/master/CHANGELOG.md

over 1 year ago