Proprietary software often comes with a licensing agreement that imposes restrictions on the use, modification, and redistribution of the software. This contrasts with open source software, which is freely available to use, modify, and distribute. Freeware simply refers to software that is available for free, and could be either open source or proprietary, while shareware is a type of proprietary software that is offered for free on a trial basis with the intention of selling it after the trial period ends.