Deployables are different from grenades in that they're usually multi purpose useful tools. From automatic weapons to "shoot to work" to zombie activated there are a lot of different deployables with quite a few perks to boot. They recharge nightly meaning you can place one and have another for the next night. The deployables are much stronger and more expensive than grenades and so they usually take much longer to restock for example the sentry gun takes 3 nights until you get another.
Here is a list of all the Deployables in the game there are 16 in total:
All items (16)