There are several other notable options - SoundCloud's LHM, Facebook's online schema change tool, etc. They all have their different quirks.
(And as modern MySQL releases get better online DDL support, become less and less critical - though still useful for all of those edge cases where native lockless online DDLs can't work yet)
(And as modern MySQL releases get better online DDL support, become less and less critical - though still useful for all of those edge cases where native lockless online DDLs can't work yet)