I use these things A LOT! They are great for temporary builds, as you can very easily disconnect and reconnect wires using them. They are also certified for permanent installation. Best of all- they will connect everything from 20AWG “alarm” or “network” cable up to 10AWG, mix and match, stranded and solid! They are good for low voltage as well as 120v.

Update: There are actually two types:
221-41x – 22-12AWG
221-61x – 20-10AWG
Most home centers have the 41x (22-12AWG) version, which is also the best one to use for holiday light and general home applications.

They are not water/weather resistant, so they do need to be used in some kind of enclosure for outdoor work, but they are a great alternative to soldering, crimping, or old-school wire nuts.

WAGO recently re-designed the Lever Nuts. They used to be a bit blockier with smaller orange levers. I used those previously and loved them. You will see them on some of my older builds, or re-used for test builds.

Older WAGO Lever Nut Style
The older style of WAGO Lever Nut

You can buy them at almost any hardware store, home center, electrical supplier, or of course through eBay and Amazon. In fact- since they were re-designed, the older style ones can be had very cheaply in huge quantities as of this post.

There are Chinese-made rip-offs, of course. I’ve used some of them for low-voltage applications and car audio stuff. They tend to have smaller levers that are harder to work with and use flimsier plastic bodies. They may work as good as a WAGO, at least for a while, but I don’t personally trust them.