Blues did a great job covering the whole scope of an IoT developer. This post suggesting further extending this coverage to include sensors simulation.
I have long experience developing Cloud Apps (the right hand side of your diagram pictured below)
and very little experience with entities shown on the rest of this diagram, being interested to prototype the complete solution, having some “adopted” methodology that replaces the set of sensors with a sensors/devices simulator would be simply terrific.
The reference to https://mongoose-os.com is provided only to better define the context of this discussion. I could have selected https://ubidots.com/ or https://golioth.io/. Both these vendors seem likely to be Blues competitors, not partners.
My plan includes the creation of several complete applications, starting with a healthcare domain (I spent nearly 12 years in that space, and created one of the worlds first Patient Portals in Whatcom County, WA in partnership with WA State Government , Microsoft and RW Johnson foundation). This app (as I understand it now) was at least 15 years ahead of its time, suggesting that creating an open source implementation might just be the right thing do to today.