Rank and File is not scale specific though the author used 28 mm figures. It can handle games with lots of units on the table with ease. It is not a simulation set of rules but more of a 'fun game' set of rules, easy to learn, easy to use - and easy to modify if you desire. I have added on command and control which the rules don't have. That has been the only real complaint I've heard against the rules, no command and control. That ease of use, easy to learn means good for conventions - which in this part of the world means full participation games.
The turn sequence might seem odd at first but once you realize how it works, I actually find the sequence the most sensible I've encountered in nearing 40 years of regularly gaming.
Designed for multi-figure basing but easy enough to use with single based figures (which I don't get for large games, multi-based figures dramatically speed play). Units can be from 4 - 10 stands of figures for either foot or mounted. Artillery are 'single stand' units with slightly different rules (but not in any difficult way). Lose a stand for every 3 casualties (no matter how many figures on the stand) and such losses slowly degrade the unit's ability to stay in the fight. Once a unit losses half strength it can no longer rally. This really avoids the fight-to-the-last-figure mentality so common with wargamers.
Morale is key and the rules state to be measured using a d6 but I recommend - and the author approves - using a d8 which gives units greater staying power on the game table. Though for a faster game, keep the d6 version.
I find units with six stands to be a good balance - and nicely fits with my collections.
Here in my piece of the world, Northern California, USA, these rules have become a favorite for a lot of people and are probably the most popular, certainly within the group I game with they are a go to set of rules. (Of course, many wargamers are inveterate tryers of new rules, what I call the 'windsock phenomena': 'look, new rules, let's try them - even though they are not play tested hardly at all, have a hundred typos, and don't play very well. But they're new! Oh, wait, look a new set of rules, let's rebase everything again and try those. And, oh, wait, a new set of rules..." Rinse and repeat. My response to that is to avoid new rules as much as possible and stick with what works. For me that is Rank and File - which is designed to be used for conflicts from 1740 - 1900, basically the Horse and Musket period. Some people complain about rules that do that but I suspect most of the complainers have a set of rules they are either selling or really like and don't want to change (which I truly understand). My only alternative to Rank and File is Fistful of Lead, especially the Bigger Battles version. Those two sets of rules pretty much cover all the gaming I can imagine wanting to do. FFOL can be used for larger battles I suppose but Rank and File a better choice in my opinion.
I guess I should also point out that I am a leading voice against 'too many sets of rules', it being one of the biggest challenges in the hobby in my opinion. How does a new person to historical gaming get a sense of where to start when bombarded with so many different rule sets. As I've said elsewhere, if the rules situation that exists today existed when I got started, I wouldn't have walked away from the hobby - I would have ran full tilt away from the hobby. It is just unhealthy for the growth of the hobby. Sure, nothing wrong with choice - until it causes stasis. To that point, since we've put more focus on this one set of rules we've started getting more people who show up to play coming back since they have a better sense of what to expect.
Okay, stepping off my soap box now.