Trade Stimulators were small countertop amusement devices - typically modeled after slot machines.
These games would vend something similar to a gumball or other small trinket - to skirt gambling laws.  The gameplay was typically gambling.  If the slot came up a winner, you would notify the bar owner or shopkeep and win a free beer or other prize, or in some cases, a payout.
For amusement only, indeed!