It depends on if the font designer wants to add more weights or not.
Can you provide a project example for this case
You need to install the font Montserrat first to get this. You can find this in Google Fonts.
Project example for this case (drag and drop the image):
There are lots of variable fonts in Google Fonts, but my favorite ones are Montserrat and Rubik.
Then you need to go into your browser settings, and change the monospace font (if you want the default monospace font to be Montserrat)
Idk know why, it's working without installing the font !
(this font is missing from the windows font directory)
Whatever font you have already, may actually also have different weights.
Sometimes fonts take a little while to actually reach the Windows font directory. I recommend restarting your computer for it to show up?
Actually, when the font is installed, it will instantly reach the Windows font directory.
Hmm. For my computer, it's a little different. 
what is that at the bottom
A silly cursive font on Apple and Google systems.
It's called Zapfino. Zapf is a well-known font foundry, probably best-known for Zapf Dingbats, which has come with all Postscript laser printers since forever.
That's not the whole font, just the sample that FontBook shows you.
Just to clarify, my Mac has 564 fonts installed. (I no longer remember how many of those came with the vanilla OS.) But half of them are barely-distinguishable sans serif, and another half are non-Latin-alphabet fonts that @loucheman's script can't display because their names are in the Latin alphabet. So I just picked out some of the highlights.
Could Jens include a list of fonts that could be used instead of monofont (?).. This font list would be available regardless of the OS...
You mean as the standard font Snap! uses for everything? That's Arial, not a monospace font. If you mean something else, please explain.
I really wish Jens had picked some other font, because it's really hard to distinguish among capital i, lower case L, and vertical bar. Almost any serif font would do, but there are a few sans serif fonts whose designers at least tried to make those glyphs distinguishable. But pretty much every computer has Arial (I remember not so long ago everyone was saying that Microsoft was dead because the web made operating systems unimportant...) and so we don't have to download a font when you start Snap!. And changing the font geometry breaks everything, such as the vertical extent of the font within a block picture. To make Snap! robust against font changes would take effort better put into, you know, multimedia and AI and all that.
I don't know, something else besides Arial...
Actually, from my time working on snapblocks, I found out the snap actually uses Verdana for blocks, and Helvetica or Arial for inputs (I don't know why they use different fonts). Pretty sure if you don't have Verdana installed, it does use Arial though.
Here's a script pic (from my ipad, apparently my phone doesn't have Verdana).
Huh, I learn something every day.
I've been playing around with it. The capital Z in Zapfino doesn't look like the regular capital Z in the FontBook font sample, so I figured it had to be an alternate glyph. And indeed there are alternate capital Z glyphs:
of which the top-right one looks kinda like the one in "Zapfino," but that bottom swash isn't nearly long enough. Turns out the font's logo is a single glyph:
