These are double-sided FR4 prototyping perfboards with a grid of plated through holes at 1.27 mm pitch (0.05”). These boards awkwardly straddle the border between THT and SMT. While a 6 x 8 cm piece of ordinary perfboard would be a fairly limited working area, bear in mind that halfing the pitch quadruples the number of plated through holes so prototypes can be much more efficient with the space.
