Full license text is included in SDK package of AltSDK.
All editions require one license per seat (per indie team for Advanced Indie).
If you develop any framework (Game Engine, GUI Framework, etc.) with any part of AltGUI / AltSketch, your framework users must purchase a license of AltSDK. It's because AltGUI / AltSketch can be used only in developing end user applications (Games, Applications, etc.). AltGUI / AltSketch can not be reselled in any form to another develop. It can be distributed just only as part of end user application/game.