Here is the full list of all 19 Race.a.bit achievements.
Win a bronze medal on at least one official track.
Win bronze medals on at least half of the official tracks.
Win bronze medals on all official tracks.
Win gold medals on all official tracks.
Upload a track you created.
Upload ten tracks you created.
Upload twenty tracks you created.
Beat a friend on a track you created.
Race on ten community tracks.
Race on fifty community tracks.
Race on a hundred community tracks.
Rate a community track.
Rate twenty community tracks.
Rate fifty community tracks.
Fall of the edge.
Explode.
Challenge a friend.
Rank in the top 10 of a highscore list.
Unlock all achievements.