xenodm is the X Display Manager, since OpenBSD 6.1!
xenodm is a simplified fork of xdm, lightweight, more secure, rid of XDMCP support, because of many security vulnerabilities. It support only the BSDauth code used in OpenBSD.
On OpenBSD 6.5, xenodm is absolutely necessary to start the X server, because it no longer has setuid rights enabled by default.
Details: