Is a gem ready for Rails 4 or 5?

Rails 4: 582 ready, 38 not ready, and 435 unknown
Rails 5: 92 ready, 10 not ready, and 953 unknown
Name Status Rails 4 Notes Rails 4 Status Rails 5 Notes Rails 5 Status or notes updated
font-awesome-rails ready

https://github.com/bokmann/font-awesome-rails/issues/45

ready

since version 4.5.0.1

about 2 years ago
coffee-rails ready

_

ready

since gem version 4.1.1

about 2 years ago
brakeman ready

Tests show that it works under rails '4.0.0.beta1'.

ready

since gem version 3.1.5

about 2 years ago
teaspoon ready

_

ready

since version 1.1.5

about 2 years ago
sass-rails ready

_

ready

since gem version 5.0.5

about 2 years ago
seed-fu ready

since version 2.3.0

ready

since version 2.3.6

about 2 years ago
premailer-rails ready

since version 1.3.2

ready

since version 1.9.2

about 2 years ago
acts-as-taggable-on ready

since version 2.4.1

ready

since version 4.0.0

about 2 years ago
activerecord-session_store ready

version 0.0.1 is ready

ready

since gem version 1.0.0

about 2 years ago
default_value_for ready

since gem version 3.0.0

ready

since gem version 3.0.2

about 2 years ago
rspec-rails ready

apparently full support since gem version 2.14.0 (source)

ready

since version 3.5.0

about 2 years ago
bullet ready

works

ready

since version 5.2.0

about 2 years ago
action_access ready

Built for Rails >= 4.1

ready

Added explicit support for Rails 5.

over 2 years ago
scenic ready

-

ready

-

over 2 years ago
high_voltage ready

-

ready

since version 3.0

over 2 years ago
factory_girl_rails ready

-

ready

since version 4.4

over 2 years ago
factory_girl ready

https://github.com/thoughtbot/factory_girl/blob/master/Appraisals#L9

ready

since version 4.4

over 2 years ago
suspenders ready

-

ready

from version 1.41

over 2 years ago
paperclip ready

since gem version 3.5.1

ready

since version 5

over 2 years ago
clearance ready

from version 1.0.0.rc7 (source)

ready

from version 1.13

over 2 years ago