Aspen plus is a software of Aspen tech.
Hysys software used to belong to Aspen tech, but later (around 2004) Aspen sold part of hysys to hypotech, and later (just sold in 2008 or 2009) hypotech sold hysys to Honeywell, and Honeywell renamed HYSYS Unisim.
That is to say, the former HYsys and the current Unisim are the same thing, basically the same, but the manufacturer has changed.