Offtopic: does anyone know any easy to use task scheduler software?

It's like a to-do list/task manager software, but allows you to create "relations" between each task, the whole dependency is a Directed Acyclic Graph, then the app automatically do a topology sort and tell me where to start, tell me the most important task node, and find the optimal route. A Gantt chart is a plus

Both desktop/web app would be OK. TIA