Over the years, there have been some interesting ways thought up to create a more portable form of mitre box. Here are two. First, the Sandvik 232 adustable mitre saw guide:
It is designed to allow two cutting positions: left and right.
Remove the coarse-threaded plastic hand bolt, and you can arrange the guide to cut mitres on the left side of the board:
Below, in use, with the guide clamped to the workpiece:
The guide itself will take a regular hand saw, but not a back saw, which is a drawback as a regular saw doesn't have as rigid a blade:
Mine was originally sold in the Beaver Lumber chain of stores, for $14.49. It's no longer available.
Now to the second tool. In 1960, Robert I. Johnson of Eugene, Oregon was awarded U.S. patent no. 2,956,598 for a "portable mitre box." Eventually, it became the awkwardly named "Anglerite" (which would have benefited from a hyphen) produced by the Nielsen Saw and Manufacturing Company of Eugene, Oregon. That company was around in the 50's and 60's but has left no presence to be captured by the Web. The tool was presumptuously identified as a "Model 350" but may have been the only tool offered by the company. I certainly have been unable to find any other offerings.
It's also designed for a regular hand saw. The guide is simply too wide to permit anything other than a huge back saw to fit with enough blade clearance. So, a drawback.
Unlike the Sandvik, it has another adjustment for making compound mitre cuts:
Also, unlike the Sandvik, it comes with a built-in clamp, which unfortunately leaves much to be desired.
My conclusion: both tools are too gimmicky to serve the purpose for which they were intended. Neither is rigid enough to permit the user to cut accurate mitres. While better than trying to cut mitres without a guide, a carpenter would be much better off with a simple mitre box.