This feature would be fantastic for creating a modular environment. The passing of parameters between flows and essentially creating the ability to make functions would make flows an irreplacable asset to my work.
We are now working on this and will release it in the next couple of months.
Hmm. I just tried and was not able to replicate your issue with "e-mail with options" action. I was able to send out a bunch of e-mails all at once, as long as I set apply to each to run in parallel. Guess you do max out at 50 simultaneous e-mails, but I can't imagine a scenario where more would be required (or you couldn't find a way to split the process into multiple loops).
Anyway, glad my post helped you solve your issue.
Mmm, others have also reported it works ok, and mine did work for a while too. Then it just stopped - immediately after I handed it over to my customer for UAT! Hence ranties unsued.
Anyway, the http web services approach I'd always mentally confined to using with Azure Logic Apps, Functions, etc.. Now that it seems reasonably usable and robust in Flow in opens up new architectures for doing this sort of thing in Flow, and I wouldn't have come to it without the issue and your comments.
So all's well that ends well.
As covered in the comments this is currenly supported via HTTP request/response. However, we are planning on adding a more native way of integrating flows together.
Why couldnt you just use a table in SQL or SharePoint or Basically any table ?
Flow Number 1 runs and updates [Table] with # of flow that should run next Ex. #2
Flow Number 2 triggers becouse the table was modified and #2 was entered in the field
Basically , use a table where you have all your flows triggering when the table gets modified. Within Each flow , update the [Table] with whatever flow number you want to run. Of course , each flow would need to getitems and only run if the number in the field equals whatever number the current flow is.
This is not as efficient as being able to call a flow directly in a flow, but it does allow modular flow development and reusable flows.
This feature would be really great!