The best alternatives to CreoPop are Massless Pen, PaintCube, and 3Doodler. If these 3 options don't work for you, we've listed a few more alternatives below.
PaintCube is web-based 3d texture painting app that allows you to create and export textures for your 3D models, a range of familiar painting tools that let you paint directly onto your models in 3D space allowing a seamless UV workflow