Historically, PaintTool SAI was offered as a freeware application when it was first released. However, over time, the software evolved, and the company began to offer it as a paid product. As of my last update, PaintTool SAI is no longer completely free to use.
Systemax is a small developer—likely one or two people. If you love the tool, buying a license supports the continued development of SAI 2. is paint tool sai free
SAI Ver. 2 (often called SAI 2) is currently in a long-term public beta. To access the beta, you must already own a license for SAI Ver. 1. The license key works for both versions. Historically, PaintTool SAI was offered as a freeware