This sweeping science-fiction saga delves into the rich Halo universe with 7 exciting stories including tales of Master Chief's mysterious origins, the Spartans' advanced combat capabilities and the tense rivalry between Spartans and Orbital Drop Shock Troopers (ODSTs). 
(Source: Warnervideo.com) 

1) Origins Part1 (STUDIO 4℃) 
2) Origins Part2 (STUDIO 4℃) 
3) The Duel (Production I.G) 
4) Homecoming (Production I.G/BEETRAIN) 
5) Odd One Out (Toei Animation) 
6) Prototype (Bones) 
7) The Babysitter (STUDIO 4℃) 
8) The Package (Shinji Aramaki) 
 
Note: Since The Package aired in two parts on Halo Waypoint and Origins has two parts the total number of episodes is 9 for the 7 stories. 5 of the 9 episodes aired online, making Halo Legends technically an ONA.