Gen77, or Generation77, is a new generation of kids with genetic enhancements. Most of them are associated with or part of the Doomsday Group, and are previewed at the end of FANG (when Max goes through Fang's stuff on his laptop); they are formally introduced for the first time in ANGEL. (The Flock is said to be part of Generation 54, and the Erasers are part of Generation 17.)
When the Flock (Max and Dylan, more specifically) checks out a school built for Gen77 kids (at Jeb Batchelder's and Dr. Hans's requests, and partially encouraged by Dr. Martinez), they are ambushed by the Gen77 kids there. Most of them are young, around Angel's age.
Jeb and Dr. Hans try to convince Max to lead this group, as she will become the new, sort of "queen of the world" when the world changes.
Unlike previous generations of mutants, very few Gen77 members are recombinant-DNA life-forms. Most of them appear to be human, and each member's power varies. Most of them seem to have enhanced physical features, such as Kate (who has super strength) and Star (who has super speed that surpasses that of even Max).
The most noticeable members of the generation are the spider-eyed kids (kids with eyes around their heads, giving them a 360-degree view…although they can't see from above) from the school built for the Gen77 members. Jeb and Dr. Hans mentioned that some members are heat-resistant, and others are telekinetic.
It is unknown if Beth (an organizer for the Doomsday Group) is a member of this generation, let alone a mutant, because there is little proof that she has a power like Angel's.