Manage Your Tasks - TaskWarrior
if you live in the command line world, like me, you would look for and more tools that work better in the terminal, taskwarrior is a really good task manager, it adopt the linux commandline-fu, and it wont take time untill you get use to it.
depend you distro, the command will be different, but you should know your package manager, arch is as easy as:
# pacman -S task
fedora would be like
# dnf install task
# apt install taskwarrior