The O'Saasy License Agreement is a free software license granted by 37signals LLC that permits use, modification, and distribution of the software with the requirement that copyright notices be preserved in all copies.

The license explicitly prohibits licensees from using the software to create competing SaaS or cloud services where the software's functionality is the primary value offered to third parties. The software is provided "as-is" without warranties, and the licensor assumes no liability for damages or claims arising from its use.