The reign of analog video represents a strange time in video technology because while there was certainly rapid advancement, most of the available platforms were completely incompatible with each other, making the world of analog video a confusing place for the average consumer. 

In the home camcorder department 8mm technology rose to prominence mostly because the size of the 8mm cassette fostered the production of small, easy to use, hand-held camcorders.  Unfortunately, home video was dominated for quite some time by VHS and the two platforms are not compatible.  The need for an 8mm video adapter is self evident. 

There were VHS camcorders prior to 8mm, but the VHS camcorders were so large, they required a tri-pod or shoulder mount to operate.  They were not very user friendly.  Still, because VHS showed up first (along with its vanquished foe Betamax), the VHS format became the standard for home video entertainment, and VHS recorders/players (VCR's) became standard household electronics. 

When 8mm came out, it immediately gained a following in the camcorder market but never made much progress in the home video department.  Since VHS and 8mm were roughly the same in terms of quality and price, there was really no significant incentive to make the switch.  Most movies were already available in VHS, so converting to 8mm was impractical.  The result of this phenomenon was a large amount of people with 8mm camcorders and incompatible VCR's.

Of course, you can always convert 8mm to VHS if you play the 8mm directly on the TV through the camcorder, and simultaneously record on your VCR.  This can be a tedious task, and if your 8mm camcorder is broken, you're in trouble.  For this reason, many people end up looking for an 8mm video adapter.  Unfortunately, these types of adapters don't really exist.

From an engineering standpoint, it is physically impossible to play 8mm tapes on a VCR.  The two formats use different sizes, different capturing methods, and different playback methods for both audio and video. 

Most adapters on the market today are designed to convert VHS-C tapes (which are roughly the same size as 8mm tapes) to VHS.  8mm cassettes do not work properly in these types of converters.  So, while it is possible to transfer 8mm tapes to VHS or DVD, there is no specific 8mm video adapter.