pound of black powder inside a wooden shell with a fuse can make a simple but potent explosive. You can use an action to set and light one or more black powder charges which explode at the beginning of your next turn. Any creatures or objects within 10 feet of the exploding charge must make a DC 14 Dexterity saving throw, taking 1d6 force damage and 1d6 fire damage on a failed save or half damage on a success. Increase the explosion’s damage by 1d6 force and 1d6 fire for each doubling of the number of charges set beyond the first.

A bell is a directly struck idiophone percussion instrument. Most bells have the shape of a hollow cup that when struck vibrates in a single strong strike tone, with its sides forming an efficient resonator. 

You can use an action to spill these tiny metal balls from their pouch and cover a level, square area that is 10 feet on each side. A creature moving across the covered area makes a DC 12 Dexterity saving throw or falls prone. A creature moving through the area at half speed doesn’t need to make the save.

An abacus, also called a counting frame, is a hand-operated calculating tool.