If you do not prefer to use WLM then you have to build your on Queue Management using database. There has to be some mechanism for managing the state of the work items. if not WLM, then it will be your custom queue which can be built but needed additional logic and implementation.

I am not sure why you don’t prefer to use WLM when it is already available as part of the platform.

As @DS78  mentions the problem of queue management outside of WLM is non trivial. 

If you had a list of available bot agents, you could use APIs to track if the Bot Agent is available, then use the Deploy API to send the task to that… 
 

…. But that is what WLM is doing with much more logging, state trackings, and better control.