Chainmail (or D&D Chainmail, as it was known to differentiate it from the proto-D&D miniatures game "Chainmail"), was published by Wizards of the Coast in 2001, and contained some notable alumni in its production: Chris Pramas, Skaff Elias, Adrian Smith, Mike McVey, and Jason Soles to name a few—not to mention all the sculptors you'd no doubt recognize.
So what was so cool about Chainmail? It was effectively D&D 3rd edition turned into a miniatures game. You assembled a warband of figures that generally numbered anywhere between three and seven figures, and you maneuvered and spelled the shit out of each other! It had a really innovative command system, where your commanders could issue orders to troops. Your commanders had a number of command points that they could expend to move their basic troops around and maybe even make them fight a little better.
It had the perfect mix of casual and competitive rules and attitude that I've not seen matched in any miniatures game since. The rules were such that you could assemble a warband of synergistic models and conduct your battles in a strategic manner similar to what you may see at an X-Wing or Warmachine/Hordes tournament. But if you weren't a competitive gamer, then the sheer amount of scenarios they released—combined with the campaign that was contained in their first supplement—meant that you could play thematic games that focussed on a story.
Really, it still amazes me to this day the sheer amount of scenarios that game contained. By my count there were over thirty at the end of its run in 2003. The scenarios weren't like your typical tournament-focussed scenarios which are largely abstract, gamey, set-ups that you may see in an event's "tournament package" (though the game had these too), but they felt like these would be conflicts in a fantasy world.
These scenarios were contained in the rulebook and over the course of four supplements. These supplements not only contained scenarios and rule updates, but new rules on environments (fighting in the underdark), new spells your models could learn, and the stats for the new wave of models. They also contained more of the ongoing story about these empires and hordes fighting over the sundered essence of the dead god of war Stratis.
Back in 3rd edition D&D, WotC wanted to focus the setting on the world of Greyhawk. In order to make a miniatures game where there were stakes to the storyline and players' victories they set the game in the Sundered Empire in the western part of the main continent on Oerth, and introduced new characters and factions.
The models were good too. Some of them were pretty typical of the early 2000s, non-Citadel, quality that you saw among the miniatures spectrum, but it had the best range of gnolls I've ever seen. It also had the coolest owlbear.
Anyway, that's really all I wanted to say on the subject. The game's long dead, having been replaced by the pre-painted figures and simpler miniatures game in 2003. I enjoyed that one too, but it was no Chainmail.