ZeroTrust Vendors
ZeroTrust Network Access (ZTNA) / BeyondCorp / Continuous Adaptive Risk and Trust Assessment (CARTA)Vendors of ZTNA as a Service
As-a-service offerings require less setup and maintenance than stand-alone offerings and typically require provisioning at the end-user or service side, routing traffic through the vendor’s cloud for policy enforcement.
Akamai - Enterprise Application Access
Cisco - Duo Beyond (acquisition)
CloudDeep Technology (China only) - DeepCloud SDP
Cloudflare - Cloudflare Access & Gateway
Meta Networks - Network as a Service Platform
New Edge - Secure Application Network (Netskope??)
Okta - Okta Identity Cloud (Acquired ScaleFT)
Perimeter 81 - Software Defined Perimeter
Broadcom (Symantec) - Luminate Secure Access Cloud (acquisition 2x)
Verizon - Vidder Precision Access (acquisition)
Vendors of Stand-Alone ZTNA
Stand-alone offerings require customers to deploy and manage all elements of the product. In addition, several of the major IaaS cloud providers offer ZTNA capabilities for their customers.
BlackRidge Technology - Transport Access Control
Certes Networks - Zero Trust WAN
Google Cloud Platform (GCP) - Cloud Identity-Aware Proxy (Cloud IAP)
Microsoft (Windows only) - Azure AD Application Proxy
Safe-T - Software-Defined Access Suite
Waverley Labs - Open Source Software Defined Perimeter
Zentera Systems - Cloud-Over-IP (COiP) Access
Vendors Currently Unclassified by Gartner
May fit into one or the other above.
Illumio - Adaptive Security Platform
Palo Alto Networks - many, including Prisma Access
VMWare - Workspace One Unified Access Gateway

Cyxtera Technologies, MobileIron, Symantec, Unisys, Forcepoint, Google, Check Point, and Forescout are Strong Performers
Proofpoint is a Contender.
Sources:
Gartner: Market Guide for Zero Trust Network Access - 29 April 2019
Forrester Wave: Zero Trust eXtended Ecosystem Platform Providers - October 29, 2019
Full Reports Available from various vendors