Which Software businesses have the lowest margin of profitability?

You might need to be more specific with your question. On the one hand uou have gross margin, on the other net. They might be very different.

For example Uber is almost certainly a negative net margin (although I haven't paid a lot of recent attention. Ditto Twitter. )

On the other hand businesses can have a low gross margin, but still be profitable.

From a business point of view "margin" is a useful measurement, but be careful oc optimising for margin. (I know one business that would decline jobs if they reduced average margin, in spite of them improving profitability. )

Speculating: Twilio or any other telephony software