I've been using this app and its Android version for years (there is also one for iOS) and I've never found anything close. Too bad that the project seems to be abandoned. It's a pity, and a great loss that it was not open sourced. The app is still usable though, and I encourage you to try. Please let me know if you know anything similar. I am aware of desmos and geogebra, but I think this one is superior. Especially the graphics, 2d, 3d, vector fields and many more. Super fast, interactive, I really like the asthenic.