You might be interested in the Matthews 'Road Rags' system and 'Mini-Grip' to begin with. They include black scrims (to cut down light without diffusing it), flags and silks (diffusers) in a pair of handy roll-up pouch thingies. Scrims and diffusers are quite widely used (at least by me!) as well as large and small flags for stopping light from going where it shouldn't.
Manfrotto don't make equipment to quite the same degree of robustness as Matthews, but the price is more attractive and it is still very good stuff. I have a few super clamps with friction arms (which I prefer to the magic arm) for holding things in odd positions. They make grip heads and grip arms as well. Those can be rigged to hold the flag, scrim or diffuser on the same stand as the light. You can't have enough grip heads and arms, whether they be Arri-badged, Matthews, Manfrotto or whatever. Matthews make the single most useful lighting stand in the world, the magic stand with the runway base, and Manfrotto make (or made) a similar thing at a much lower cost, but I can't find it on their website.
I've seen Matthews dots and fingers in the grip trucks of big productions here in NYC, but I've never seen them used, and I've never asked for them. If I want that kind of control I'm much happier with black cinefoil - which is heavyweight aluminium foil. That's versatile stuff.
Lowel make a few useful, reasonably-priced light control things which are OK if you are handling them yourself. I find that grips who expect bomb-proof Matthews equipment can't get used to the lighter Lowel gear. Things like lobos, lobo arms (like a lightweight grip head and arm), maxa-mounts, tota-flags, flexi arms, tota-clamps and other names I wish that I
couldn't remember.
www.lowel.com
Best,
Helen