Book lending

I highly advocate the lending of books to your friends! It’s a great gesture of trust and a way to spread your love of books. My issue is that I always forget to whom I’ve loaned a book. My approach is to act now and not think about it later. Well, until I suddenly get the urge to read that book or want to lend it to someone else. Then I thought, there must be an online solution to this problem! But I couldn’t find one doing a quick search. Does anyone know of a great tool to better manage my physical library of books as I lend them out? I would love to hear your suggestions!