Gentoo is what ever you like it to be; that is what makes it so interesting. You always install the same distribution with rolling updates and no release versions. Gentoo can be a...
Desktop with bleeding edge 3D graphics. Choose your own desktop environment or just mix them. The possibilities are endless.
Development Station for any software you can imagine.
Embedded System, stripped down to a few megabyte and it has 11 official supported architectures.
Server with endless possibilities. A blown up cluster with distributed computing to wifi router at home, secure hardened, normal or development environment.