Tinderbox is a package building system for FreeBSD ports, based on official Portbuild scripts used on pointyhat building cluster. Tinderbox was written by Joe Marcus Clarke.
You can define multiple jails (base system versions) and multiple portstrees. The combination of jail and portstree is called a build. A Tinderbox jail is not what is understood as a jail in FreeBSD, it is in fact a given world in a chroot. Tinderbox supports automatic tracking of dependencies and only rebuilds packages that changed since last run. Tinderbox has support for email notification of failed builds. Tinderbox also integrates well with ccache.
Tinderbox is designed to easily provide package sets of ports you need, for platforms and architectures you need. Tinderbox is also excellent tool for testing new ports and port upgrades, especially for testing dependencies and packing lists. It's also useful for testing ports on various releases of FreeBSD, since you can run FreeBSD 8.X/9.X world as a jail on a FreeBSD 10.X host.