Contact Form 7
I just realized that I haven’t mentioned the free Contact Form 7 plugin at all in the Toolbox. Considering it’s one of the few plugins I want on just about every WordPress installation of mine, not bringing it to your attention would be an injustice.
Yeah, as its name suggests, it does contact forms. “Just another contact form plugin. Simple but flexible.” That’s how it describes itself on the WordPress plugin repository, so I wouldn’t blame you at all for thinking that basic contact forms are all it does.
No, contact forms aren’t all it does. There’s a lot of power under the hood of this deceptive little form engine. Like calculated fields; stick complex formulas in there, and you’ve got yourself a nice little custom calculator creator for your WordPress site. It natively supports online payment services like Stripe, so you can use it to receive payments. It’s got a ton of other little features (like subscriber mode, so only logged in subscribers can use forms), even third party ones, to cover here.
It’s very well-documented too. It’s got just enough oomph to turn WordPress into a simple application development platform, quite frankly. The fact that it’s totally free—no premium anything—makes it even more amazing.