Advanced Coroutines are the best alternative to standard Unity coroutines. Advanced Coroutines allow you to see coroutines' work visually so that you would always see which coroutines are running, stopped or paused with its full CallStack.
With Advanced Coroutines you can write your own version of WaitForSeconds, AsyncOperation, etc. which will work by your own rules. Also, Advanced Coroutines are much more memory efficient than standard ones, so your app will perform much quicker than ever.