I also took some time to write a script to figure out which widgets there are available in Odoo. Here's the full list (123 widgets):

'float_time', 'many2manyattendee', 'many2many_tags', 'one2many', 'email', 'mail_followers', 'mail_thread', 'many2many_tags_avatar', 'pad', 'statinfo', 'many2many', 'radio', 'website_redirect_button', 'statusbar', 'url', 'priority', 'upgrade_boolean', 'activity_exception', 'mail_activity', 'kanban_activity', 'selection', 'bullet_state', 'embed_viewer', 'pdf_viewer', 'mrp_time_counter', 'handle', 'boolean', 'label_selection', 'CopyClipboardChar', 'many2many_tags_email', 'hr_org_chart', 'res_partner_many2one', 'monetary', 'float', 'phone', 'percentpie', 'domain', 'html', 'mass_mailing_html', 'many2many_binary', 'date', 'montary', 'image', 'boolean_favorite', 'many2many_checkboxes', 'boolean_toggle', 'section_and_note_one2many', 'section_and_note_text', 'many2one_barcode', 'tax-group-custom-field', 'payment', 'kanban_vat_activity', 'dashboard_graph', 'account_hierarchy_selection', 'state_selection', 'website_publish_button', 'sms_widget', 'link_button', 'color', 'product_configurator', 'progressbar', 'daterange', 'video_preview', 'input', 'slide_category_one2many', 'field_float_rating', 'sale_order_many2one', 'gauge', 'integer', 'selection_badge', 'hr_resume', 'hr_skills', 'website_urls', 'matrix_configurator', 'section_one2many', 'kanban_state_selection', 'question_page_one2many', 'datetime', 'attachment_image', 'relative_time', 'reference', 'timesheet_uom', 'toggle_button', 'CopyClipboardText', 'font', 'char', 'ace', 'timezone_mismatch', 'text', 'many2one', 'field_partner_autocomplete', 'iban', "#{widget.options['force_submit_url'] ? widget.options['force_submit_url'] : '/mail/chatter_post'}", 'password_meter', 'iot_picture', 'lot_barcode_handler', 'picking_barcode_handler', 'barcode_handler', 'appointment_employee_url', 'twitter_users_autocomplete', 'social_post_preview', 'signature', 'percentage', 'Many2one', 'deprec_lines_reversed', 'json', 'back_arrow', 'tablet_image', 'mrp_pdf_viewer_no_reload', 'mrp_embed_viewer_no_reload', 'filters', 'documents_kanban_color_tags', 'timesheet_timer', 'color_picker', 'hierarchy_kanban', 'marketing_activity_graph', 'call_center', 'social_kanban_field_stream_post', 'social_kanban_field_emoji', 'social_text_emojis', 'contact_sync', 'iot_realtime_value', 'field_float_scannable'