Any information about this unit? It seems like a very well built auto transformer but I can't seem to find any documents regarding this unit.
These sort of units were typically used in school labs. They were intended to be fairly safe to use and also fairly bulletproof (thermal trip). The were designed to drive a lot of different loads, including lamps and motors - hence the variac and AC / DC output (unregulated).
These days, I suspect that health and safety has taken more of a hand, also the need for closely regulated outputs for logic circuits etc, reducing the energy capabilities of modern units.
The variable mains (not sure if that's direct or transformer isolated) and beefy isolated 0-22.5V AC outputs will be useful as-is for general fault finding. The unregulated DC output is of some use, but will need a post-regulator to use it for anything electronic and sensitive.