diff --git a/lib/addons/custom_commands.rb b/lib/addons/custom_commands.rb
new file mode 100644
index 0000000..aac5988
--- /dev/null
+++ b/lib/addons/custom_commands.rb
@@ -0,0 +1,180 @@
+# frozen_string_literal: true
+
+# Custom Commands: Add custom "echo" commands, to post a text message
+#
+# For example, "!hello" might print:
+#   "Welcome to the channel! You can follow [this link](link) to visit
+#   our website!"
+
+module Chronicle
+  module Matrix
+    # Add addon-specific commands to the allowed commands array
+    add_allowed_commands(%w[addcommand modcommand remcommand])
+
+    # Add a custom command
+    #
+    # @param commander [CustomCommander instance] The CustomCommander to work
+    #                  with
+    # @param client [Matrix Client instance] The client to work with
+    # @param message [hash] The message data from Matrix
+    def handle_addcommand(client, message)
+      msgstr = message.content[:body]
+                      .gsub(/!addcommand\s*/, '')
+                      .strip
+
+      room = client.ensure_room(message.room_id)
+
+      commander = CustomCmd.commanders(message)
+      res = commander.addcmd(msgstr)
+
+      room.send_notice(res)
+    end
+
+    # Modify an existing custom command
+    #
+    # @param message [hash] The message data from Matrix
+    def handle_modcommand(client, message)
+      msgstr = message.content[:body]
+                      .gsub(/!modcommand\s*/, '')
+                      .strip
+
+      room = client.ensure_room(message.room_id)
+
+      commander = CustomCmd.commanders(message)
+      res = commander.modcmd(msgstr)
+
+      room.send_notice(res)
+    end
+
+    # Remove an existing custom command
+    #
+    # @param message [hash] The message data from Matrix
+    def handle_remcommand(client, message)
+      msgstr = message.content[:body]
+                      .gsub(/!remcommand\s*/, '')
+                      .strip
+
+      room = client.ensure_room(message.room_id)
+
+      commander = CustomCmd.commanders(message)
+      res = commander.remcmd(msgstr)
+
+      room.send_notice(res)
+    end
+
+    module CustomCmd
+      require 'json'
+
+      @@commander_instances = {}
+
+      def self.commanders(message)
+        msgid = message.room_id
+
+        unless @@commander_instances.keys.include?(msgid)
+          @@commander_instances[msgid] = CustomCommander.new(msgid)
+        end
+
+        @@commander_instances[msgid]
+      end
+
+      class CustomCommander
+        def initialize(msgid)
+          # build custom commands DB in memory
+          @msgid = msgid
+          @custom_commands = read_commands(@msgid)
+        end
+
+        # Add a new custom command
+        def addcmd(message)
+          command = message.slice!(/\w+\s+/).strip
+
+          return cmd_add_error(command) if verify_commands(command)
+          
+          @custom_commands[command] = message
+          save_commands(@msgid)
+
+          "New command saved: !#{command}"
+        end
+
+        # Modify an existing custom command
+        def modcmd(message)
+          command = message.slice!(/\w+\s+/).strip
+
+          return cmd_mod_error(command) unless verify_commands(command)
+          
+          @custom_commands[command] = message
+          save_commands(@msgid)
+
+          "!#{command} modified."
+        end
+
+        # Delete an existing custom command
+        def remcmd(message)
+          command = message.strip
+
+          return cmd_rem_error(command) unless verify_commands(command)
+
+          @custom_commands.delete(command)
+          save_commands(@msgid)
+
+          "!#{command} removed."
+        end
+
+        # Execute a custom command
+        def runcmd(command)
+          return cmd_mod_error(command) unless verify_commands(command)
+
+          @custom_commands[command]
+        end
+
+        private
+
+        # Error message when trying to add an existing command
+        def cmd_add_error(command)
+          "This command already exists. \
+          You can modify it by typing `!modcommand #{command}`"
+        end
+
+        # Error message when trying to modify a non-existing command
+        def cmd_mod_error(command)
+          "This command does not exist. \
+          You can add it by typing `!addcommand #{command}`"
+        end
+
+        # Error message when trying to delete a non-existing command
+        def cmd_rem_error(command)
+          "This command does not exist. \
+          Nothing to remove."
+        end
+
+        # Read the existing saved commands into memory
+        def read_commands(msgid)
+          cmds = {}
+          cmds_file = "#{msgid}_custom_commands.json"
+
+          if File.exists?(cmds_file) && !File.empty?(cmds_file)
+            File.open(cmds_file, 'r') do |f|
+              cmds = JSON.parse(f.read)
+            end
+          end
+
+          cmds
+        end
+
+        # Save the existing commands to a local file
+        def save_commands(msgid)
+          cmds_file = "#{msgid}_custom_commands.json"
+
+          File.open(cmds_file, 'w') do |f|
+            f.write(@custom_commands.to_json)
+          end
+        end
+
+        # Check if a command already exists
+        def verify_commands(command)
+          @custom_commands.keys.include?(command)
+        end
+      end
+    end
+  end
+end