Since Squeak 3.6, the harvesters have been superceeded by the release team
The Squeak Foundation swiki has the official page on the harvesters. See The Harvesters (SqF)
(In short, the Harvesters is a group formed as a Squeak Foundation project to harvest fixes and enhancements submitted to the Squeak Mailing Lists, for incorporation into the main Squeak release, via the Harvesting Process.)