I'd like to nominate shawshank. I was having a lot of trouble with string cloning and fixing that through keeping all strings in one place and having references everywhere else. When I found Shawshank I was so happy, it really easy to use
Shawshank gives a simple arena datastructure and interface for interning data. It's basically an arena with maximal sharing, when you give it the same data twice it will only keep one copy. Give it some data to own, it gives you back an id to access it later. With the id you can get a borrow to data, or remove (disintern) the data.