<a href="https:&#x2F;&#x2F;rebrickable.com" rel="nofollow">https:&#x2F;&#x2F;rebrickable.com</a> - A LEGO database that shows you which sets you can build from your existing collection, also includes thousands of fan-submitted designs.<p>I guess it would only loosely be called &quot;passive&quot; as I spend a lot of time on it. But, I can take vacations and it continues to earn... for a while :)