I haven’t used Chameleon, but it seems to do some stuff like change the user agent that JShelter doesn’t do. I’d assume it’s more useful to get around a site designed for a specific browser or operating system.

JShelter isn’t mainly for spoofing, it’s about blocking a bunch of potentially harmful advanced javascript features, often used for tracking. Any spoofing is mostly to keep sites working with the missing javascript features.

I have it installed on one of my browsers. I wouldn’t recommend using it unless you’re willing to tweak the settings for new sites you visit, because I’ve had it break sites pretty often with the default settings.

There’s also Arity. It isn’t the best interface, but it has functions, variables, and graphs.

I was also using Unitto for unit conversions, but apparently the creator doesn’t want forks or for f-droid to host it, so I’m looking for another one.