These are remarkably inexpensive rules from Wargame Vault which remind me of some of the old card collectible games, but using figures and also some scenery if wished. They are also billed as solo rules (although 2 can also play) and follow a very simple set up of three forward zones for each army, each having a unit in each zone, with 0-3 units in reserve, which can move into any vacant forward zone should it become available owing to one of your advanced units being defeated. You can choose a set from  many different periods. As there are only 6 bases max per side these rules are ideal for 6mm or smaller as that still gives the impression of an army. As an example, Dominion of Pike and Shot covers the Italian Wars, through to the post ECW period, with a large number of very straightforward army lists for the various periods. The reason I give this set as an example is that there is an accompanying ECW campaign available for free, also on Wargame Vault. It takes place over one year in Lincolnshire, has a campaign map, a way of determining when and where a battle takes place, with potential battlefields illustrated (the optional scenery), opportunity for interference by Manchester for Parliament or Newcastle for the Royalists, a potential siege of Bolingbroke castle and the necessity of Parliament to keep Hull supplied. Battles are very brisk and the whole campaign can be fought in a couple of hours, so could make for an entertaining evening at home or down the club. 

I have seen a few write-ups around the Internet, they do look mildly interesting. Where they billed as a solitaire game simply by virtue of having few units, or are there specific solo mechanisms?

Not really sure as I play all my games solo. They are definitely described as solo, but I see no reason that there cannot be two players. The game layout reminds me of the Gettysburg and Shiloh collectible card games from about 20 years ago. I think half a dozen bigger than normal bases would work well with 6mm figures. I use 75mm wide bases, so a dominion battlefield would be 30-45cm square.

It's also a good way to get a game in with your first painted units, whilst building forces for bigger games like BBB, Polemos and Hail Caesar, after all, the rules are base agnostic and one unit doesn't have to be one base.