Which partitioning program does Ubuntu use during installation?

Which partitioning algorithms use ubuntu during the installation, is it also available as a standalone application or command? Is it gparted?

The ubuntu installer uses parted - for the most part; The parted program in turn uses fdisk to create and modify partition tables and mkfs to create file systems.

GParted and its equivalents are merely front-ends to the linux partitioning tool kit. The Ubuntu installer is the same. It's a layer on top of parted and it executes it in the background, providing an easy to use abstraction of the plumbing behind it. The installer uses other programs, like resize2fs -to resize file systems - directly as well.