Physically-based animation is a mini-industry. Here's the Animats view of it.

The Old Guard

Mechanical Dynamics, Inc. (Ann Arbor, Michigan) Makers of ADAMS. Engineering dynamics since the 1970s. Well-respected. FORTRAN-based. Not easy to use. Offers consulting services, and is really more of a mechanical engineering consultancy than a software vendor.

LMS CADSI (Coralville, Iowa) Makers of DADS. The other old-timer. Again, more a consulting service than a software vendor.

The '90s pioneers

Knowledge Revolution (San Mateo, California) Makers of Working Model. The first shrink-wrapped simulation product. Great user interface, but the dynamics engine had problems. Originally priced around $500 and distributed through retail channels, but unprofitable at that price point. Company acquired by MSC Software (the NASTRAN people) and product repriced upwards of $3000.

Parametric Technology (San Jose, CA) Makers of Mechanica. Part of a full suite of high-end engineering tools Prices somewhere in five figures.

The Animation Systems

Alias/Wavefront (Montreal, Canada) Makers of Maya. The first animation system with a dynamics package that worked at all. The technology used was David Baraff's impulse/constraint approach. The rigid-body simulations tend to look too bouncy and light, since, as with all impulse/constraint systems, objects change direction instantaneously. We call this the "boink problem".

The Game Toolkits

Nobody seems to make money selling tools for game development. But people keep trying.

Mathengine (Cambridge, England) Makers of mathengine, originally positioned as a component of a game engine. Great PR, but mediocre technology. Heavily funded with venture capital (unusual for a UK-based startup), mathengine made a big splash in 1998, expanding internationally to about 90 employees. They seem to have cut back somewhat since. As far as we know, nobody ever actually used their product in a game that shipped. Free demo versions of the base product, but actual use requires negotiating a royalty deal.

Havok (Dublin, Ireland) A new company, part of Telekinesys Research Ltd. Associated with Motion Factory, which offers an elaborate kinematic game development environment.

Ipion (Munich, Germany) A smaller player, but with style. Fun web site.