software that allows you to modify or even substitute the video coming from your webcam

I'm looking for "webcam enhancement" tools.

Specific features I might be interested in:

simulated webcam — ALL software below support this, otherwise they wouldn't be listed. Each software sends its output to what Zoom/Google Meet/Microsoft Teams thinks is a physical webcam, but is actually a software-generated simulation.
face-track — automatically pan and zoom as your face moves around
chroma key — an improved version of background-blurring
share screen — be able to transmit your computer's screen as your webcam (for when the teleconference admin has disabled the share-screen feature)

Logitech Capture

I assume it only works with their cameras that are listed halfway down? The cheapest one is $70.
The UI looks like a really nice balance — having a fair bit of functionality, but not so much that neophytes will struggle with the UI.

OBS Studio — powerful, but its large feature-set features means it has a little bit of a learning curve

There are many help videos online about it. Because it's free (open source), it is very popular, so a lot of content gets created for it.
specific features:
- simulated webcam — use the Virtual Camera output [how to video]
- face-track — use the Face Tracker plugin
- share screen — OBS Studio lets you change between sources, with some relevant ones being: Display Capture, macOS Screen Capture, Game Capture, Window Capture, Browser, and even Media
- chroma key — use the Chroma Key Filter

XSplit VCam

Its face-tracking feature is called "auto framing".
Subscription is $30 / year.
Its UI looks pretty straightfoward. I might even say it's 'simple'.
TODO — Does it support actual chroma key?
- It used to be on the "features we're considering" list, but that URL is now dead, and I'm not sure.

YouCam

Its face-tracking feature is called "Auto Zoom Face Tracking". But does it have chroma key/green screen functionality?
$15 monthly, or $40 annually

webcam-mods — Linux-only

AlterCam

This does provide greenscreen functionality, but I don't think it does face-tracking.

SparkoCam — I'm not sure if it does auto-pan-zoom based on face-tracking. (but it does say it uses face-tracking for its TikTok-like effects) It also looks fun to use!

Magic Camera — not updated since 2015

some Anker webcams advertise their software as supporting "AI framing"

list of more software to research