This is the free version of Mick Tagger, limited to 100 actions per month (which are probably plenty for most casual users). Upgrade to the Premium version for unlimited actions.
Mick Tagger is the keyboard interface for Spotify. With Mick Tagger you can like a song, save it to a playlist, open the playlist or queue up more songs using just your keyboard. No mouse needed.
Why keyboard shortcuts for Spotify?
Doing anything in Spotify is a mouse intensive activity. To like a song, save to playlist etc. you have to click around the Spotify app, a lot.
Switching to Spotify to add to a playlist also means context switching. You lose track of whatever you were doing just to add the song.
Give MT a try and in a few days you'll notice operations that took minutes will take seconds.
The app is free to download (just put $0 in the box and get it), but if you like it, consider donating a few bucks.
Hope MT makes your life easier!