When IBM commissioned a typeface family for their own internal use, they also released it for general use. Clean and practical, Plex also has some style and warmth. With sans, serif and monospaced subfamilies and many weights, one might wish that many businesses relying on dull typefaces such as Arial and Times New Roman might make the switch and use something much better for free.
Another free offering, Overpass is not quite a grand as Plex, but with eight weights and true italics, it is a fine and generous offering. Very smart and highly readable, and more space efficient than Plex.