WIT Mod 1.13.2/1.12.2 (What Is That?) is a lightweight mod similar to WAILA. Think of it as a different flavor, serving a similar function but in a different way. It displays information about blocks and entities when you look at them. WIT also has an API for modders to work with. Note: The 1.13 version still has some issues, mostly due to Forge being incomplete.
A little window pops up to tell you about whatever your cursor is on. You need to be within a few blocks of the target. Some things WIT currently displays:
WIT Mod 1.13.2/1.12.2 (What Is That?)