A more complicated version, setting an array from multi-line standard out:

- name: Register the loaded modules
  command: a2query -m
  register: apache_modules_check

- name: Set an array of the loaded modules
  set_fact:
    apache_modules_loaded: "{{ apache_modules_loaded | default([]) + [ item.split(' ')[0] ] }}"
  loop: "{{ apache_modules_check.stdout_lines }}"

Another version not using a loop:

- name: Get a list of enabled and disabled features
  command: icinga2 feature list
  register: icinga_feature_list

- name: Set a fact for enabled features
  set_fact:
    icinga_feature_disabled: "{{ (icinga_feature_list.stdout_lines[0] | regex_replace('^Disabled features: ')).split(' ') | list }}"
    icinga_feature_enabled: "{{ (icinga_feature_list.stdout_lines[1] | regex_replace('^Enabled features: ')).split(' ') | list }}"