First crack

app/models/group.rb

@@ -0,0 +1,9 @@
+class Group < ApplicationRecord
+  has_many :user_groups, dependent: :destroy
+  has_many :users, through: :user_groups
+  has_many :application_groups, dependent: :destroy
+  has_many :applications, through: :application_groups
+
+  validates :name, presence: true, uniqueness: { case_sensitive: false }
+  normalizes :name, with: ->(name) { name.strip.downcase }
+end