BiitRunner

Enter an Artist, a Tempo (BPM) and hit the "Get songs!" button. It will return a list of recommendations related to that artist, matching your chosen tempo.

Click either a song or an artist to reveal "Like" and "Dislike" buttons. Liking something is equivalent to searching for it, and will add new recommendations to your current ones. Disliking a song will remove that song.
Disliking an artist will remove all songs from that artist.

By default, songs that matches half the specified tempo will be returned. This, and the tolerance can be adjusted under "Options".

If you make a mistake, click the "Undo"/"Redo" buttons. If you want to start from scratch, click the trashcan.

After you've created your playlist, it'll be available in your Spotify app.