We use HubSpot for CRM and marketing. It's a very feature-full integrated service with great appeal to RingCentral users. Similarly, I suspect that many HubSpot users would find RingCentral integration very attractive.
HubSpot has similar market capitalization as RingCentral, growing rapidly and targeting similar user base as RingCentral.
https://finance.yahoo.com/quote/hubs?ltr=1
It would be tremendously useful to have a tight API-based real-time integration between RingCentral and HubSpot so that phone calls, missed calls, voicemails and recordings can be accessed in HubSpot during or right after the call; and missed calls addressed / followed up.