I need to sketch character poses in a wireframe type of way. The characters would be performing an action, like grabbing something, so the hands are also important. The purpose is to do some training fitness material. If possible, some basic animation (not interactive), would also be helpful. Faces are indifferent, so are hair and the like, which might make the character more appealing for games, but it's not the case here.
It has been a while since I used it but Blender is the biggest and best free and open source modeling/animation. You can do *anything with it pretty much - well taking over the world might be challenging ;) but anything less than that can be done. It does take a lot of learning if you don't have any 3d modeling knowledge. I personally quite like the UI but some people have complained about it being non-intuitive. There are many great learning resources online - the official manual is pretty shiny too.
There are also many available models/animations that you can download for free - and if do to the vast array of importers you go for also download quite a few game mods that you can import to have a prebuilt skeleton, model and animations.
Full animation and timing and interaction with other objects is supported (though not exactly simple).
(minor note: I have been fairly involved with a FOSS 3rd party blender script project for TES IV Oblivion model/animation import/export - though I haven't actually done anything there for a couple years. Also IIRC I had one tinsy fix checked into the blender source as well.)
Poser combines modelling, scene construction and rendering and comes with simple models suitable for instruction posters and videos, as well as the more photo-realistic imagery usually associated with it.
It is focussed heavily on posable character models, so there is less to learn than using a fully generic modelling and rendering package.
Animation is supported.
Some free-with-the-product models have simple neutral face and hair, which would seem to match your needs. There is also a large library of poses included, so there is likely to be a good close match to any specific action/pose you need.
The rendering engine supports a variety of styles, including sketches
It takes some time to learn and get the best out of it.
There are many advanced features which you may not need.
The base version will set you back around $100, unless you can justify a discount (they are available for some non-commercial purposes).