Use adhesive curtain hooks or clips
Install a tension wire or cable across the window
Attach curtains with Command hooks and rings
Use a tension rod alternative like a spring-loaded pole
Hang curtains from a wooden dowel secured with brackets
Mount a track system to the ceiling or wall
Use Velcro strips to attach curtains to the frame
Staple or tack fabric directly to a window frame
Use magnetic curtain holders on metal frames
Hang curtains from a decorative chain or rope
Use cup hooks and a line for lightweight curtains
Attach curtains with binder clips to a wire or line