Now this is not really a tool, but I use it every day and its free (online, and the mobile is a paid app, but worth it).
When I discovered it i liked the cool artwork and gave it a go. Since then it has completely grown on me and become part of my week. I love the curated music and I know that for me, songs are such a strong memory trigger that I feel I am literally hacking my brain to recall particular weeks by just listening to the same mix tape all week. Cool and weird approach I know.
Check it out and follow them on Twitter @NoonPacific