Dose anyone know a program that has the the curve, edit, and pressure features that SAI has? I like how you can make a line and then just add points with the edit button. The pressure tool is really great too. Are there any vector based programs that are as easy to use as SAI?
I am unfamiliar with Paint Tool SAI, but the specific things you mention remind me of two apps:
Both are vector-based, have excellent brush engines, and allow simple editing after the fact (add a point, recurve etc) and both have really solid pressure systems for tablets - Affinity Designer also allows manual editing of the pressure curve of a stroke after the fact which is great for working with a mouse but still having curve dynamics; Concepts has some amazing approaches to vector based but still painterly that set it completely apart from other vector design and art programs.
Hope this helps.