Slanting letters into italic or backslant in Font by Zaweba
Horizontal shear in Font by Zaweba slants every letter between minus 30 and 30 degrees: positive for italic, negative for a backslant that leans the other way.

Slanted letters carry movement. An italic leans forward and reads as emphasis, speed or a light touch; a backslant leans back and looks deliberately odd, sometimes playful, sometimes retro. Both come from the same operation in Font by Zaweba: horizontal shear.
Shear is one of the operations in the style stack. Its slider runs from -30 to 30 degrees. Positive values lean the tops of the letters to the right, which gives italic. Negative values lean them to the left, which gives a backslant. At zero the letters stand upright. Because the change applies to every character at once, and spacing and kerning are redone after it, a single drag gives you a complete slanted alphabet.
Slant, not a separate design
It helps to know what this operation is and isn't. Shearing tilts the letters as they are. In traditional type, a true italic often has different letter shapes too, such as a single storey a. What you get here is the kind of slanted roman that type designers call an oblique. For most everyday uses that's exactly what people expect, and it keeps the slanted style closely matched to the upright one.
If you want to change individual letter shapes for the slanted version, the glyph editor lets you edit any letter. Remember that those edits belong to the whole font, not only the slanted look.
How much slant to use
Small angles go a long way. A slant of around ten degrees is enough to read clearly as italic in a paragraph. Push towards the full 30 and letters start to look as if they're falling over, which can be fun on a poster but tiring to read.
Backslants are best used with a purpose. A strong backslant has an unusual, slightly unsettling energy, so it suits short display jobs: a band name, a party invitation, a heading for something deliberately quirky. The Backslant preset gives you a ready starting point, just as the Italic preset does for the other direction.
Italic in a four-style family
There are two different ways to get an italic out of Font by Zaweba, and it's worth knowing which you want. Turning on shear in the style stack makes your main font slanted. That's right when the slant is the whole point, for a font that should always lean.
If what you want is an upright font with a matching italic for emphasis, the four-style family is the better route. It makes Regular, Bold, Italic and Bold Italic from your style stack, with an italic slant you set between 4 and 20 degrees, and links the files together as one family. That way, the I button in a word processor switches to your slanted design rather than the program faking one. In that case you'd usually leave shear switched off in the stack and let the family export add it.
Working with the rest of the stack
Order matters here, as it does throughout the stack. Shear applied before serifs means the serifs attach to slanted stems. Shear applied after them tilts the serifs too. Try both and watch the preview; the difference is subtle on some serifs and obvious on others, particularly on slabs.
Shear also combines well with width and rotation. A condensed font with a forward slant looks quick and urgent. A small slant with jitter from the rotation operation gives a casual, hand lettered feel. Vertical shear is a separate operation that moves letters up or down along the line, and it pairs with horizontal shear for more dramatic, skewed lettering.
Checking spacing after slanting
Slanted letters create new spacing problems at the edges. Pairs like "f" next to a tall letter, or a capital followed by a lowercase letter, can collide or leave gaps when tilted. Font redoes spacing and kerning after every change, but it's still worth looking at real words in the live preview. If one pair looks wrong, the kerning pair editor lets you type that pair and drag it closer or further apart, then lock it.
Slant is quick to add and easy to overdo. A light touch in Font by Zaweba gives a convincing italic, and a firm push in the other direction gives you a backslant with real character.