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