General:
* Simple
* Effortless
* Straightforward
* Uncomplicated
* Smooth
* Basic
* Elementary
For tasks:
* Manageable
* Doable
* Accessible
* Convenient
* Painless
For people:
* Relaxed
* Comfortable
* Informal
For situations:
* Comfortable
* Pleasant
* Relaxing
For things:
* Convenient
* Handy
* Practical
To choose the best synonym, consider the specific situation you're using it in.