Rofi is certainly a great choice, though it relies on scripts to customize it to your needs. These scripts can be anywhere from extremely basic to insanely complex but you have to create them.
Personaly I use it as:
- an app launcher
- a clipboard manager
- an infobar to show things like the date/time, memory usage, disk space, battery level, wifi signal…
- an omnibar to perform an internet search, quick units conversions
- a calculator for simple math
- a bookmark manager (list, open, edit, add, remove)
- a password/2FA token manager (list, edit, add, remove, autofill internet fields)
- a wifi manager
- a vpn manager