Triggered by a post on Facebook (https://www.facebook.com/groups/cake.community/permalink/673205099378177/) I started working on a method to list all the models plus their relations of a CakePHP application.

RelationsShell.php

<?php

App::uses('Shell', 'Console');

class RelationsShell extends Shell {

    var $relations = array('hasMany', 'belongsTo', 'hasAndBelongsToMany');
    var $structure = array();

    /**
     * Main method takes three arguments, the model to start with, the depth and enables output in json
     */
    function main() {
        $this->getModelRelations();
        $model = isset($this->args[0]) ? $this->args[0] : null;
        $level = isset($this->args[1]) ? $this->args[1] : null;
        $json = isset($this->args[2]) ? $this->args[2] : null;

        $result = array();

        if ($model) {
            $result = $this->getModelStructure($model, $level, $json);
        } else {
            $result = 'Please pass a model as a parameter';
        }

        pr($result);
    }

    /**
     * Returns the nested Model structure
     * @param type $model
     * @param type $level
     * @param type $json
     * @return type
     */
    function getModelStructure($model = 'App', $level = 0, $json = null) {
        $result[$model] = $this->getRelations($model, $level);
        if ($json) {
            $result = json_encode($result);
        }
        return $result;
    }

    /**
     * Get al the relations from this model
     * @param type $model
     */
    function getRelations($model, $level = 0, $current = 0) {
        $result = array();
        if (isset($this->structure[$model])) {
            $m = $this->structure[$model];
            foreach ($this->relations as $rel) {
                if (isset($m[$rel])) {
                    foreach ($m[$rel] as $key => $value) {
                        if ($level > 0 && $current < $level) {
                            $models = $this->getRelations($key, $level, $current + 1);
                        } else {
                            $models = null;
                        }
                        $result[$rel][$key] = $models;
                    }
                }
            }
        } else {
            return '[ No such model ]';
        }
        return $result;
    }

    /**
     * Get all the models and return an array with all the relations
     * @return type
     */
    function getModelRelations() {
        $models = App::objects('Model');
        foreach ($models as $model) {
            $instance = ClassRegistry::init($model);
            $this->structure[$model]['hasMany'] = $instance->hasMany;
            $this->structure[$model]['belongsTo'] = $instance->belongsTo;
            $this->structure[$model]['hasAndBelongsToMany'] = $instance->hasAndBelongsToMany;
        }
    }

}