I would also like to see an app where you could have an unscheduled conversation (language on demand).  Because I speak English and spoken English is so in demand, I try to make myself available to speak with others, even if I am not learning their language.  Of course, not everybody has time in their busy schedules, but it would be nice if more people would donate 15 or 20  minutes to speaking "on demand."  However, my experience has been most people don't take advantage of my offer.  I think they are either shy or are suspicious of my intentions.  For me, it's all about sharing language.

I have used the instant tutoring feature on italki. Of course you tend to pay a premium for this service over scheduled lessons or conversations.

Hi I try to improve my English skills too. I practice speaking on new free platform feek.live (www.feek.live). I invit you.

The hello talk app is pretty good for practicing a language, but, hello talk doesn't have a place for meeting professional teachers, hello talk is good for meeting language partners.
And, if you are looking for a teacher fast, italki has an instant tutoring feature, but, I don't know how that works, I've only scheduled lessons.