DAST stands for Dynamic Application Security Testing. DAST is the process of testing web, mobile, and API applications to find vulnerabilities/security bugs through simulated attacks.

DAST is the process of live testing an application either using an automated scanner or manual penetration testing practices.

Most developers haven't heard about DAST scanners because they are primarily used by appsec and penetration testers.

What kind of vulnerabilities does DAST find?
Most automated scanners would find critical vulnerabilities like SQL Injections, NoSQL Injections, XSS, etc.
The hard-to-find vulnerabilities like logic bugs, authentication, and authorization flaws are usually done by ethical hackers, penetration testers, and AppSec engineers. The preferred approach is to write automated test cases that can be executed as part of CI/CD.

Should developers care about DAST?
Yes, they should, since having any of the above critical vulnerabilities can lead to data breaches and punitive damages. Additionally, most DAST scanners can now be easily integrated into CI/CD pipelines, fully automated.

Pros of DAST
Tech Stack Independent: Independent of the application stack. It tests the application as a whole. All your source code and libraries at runtime are tested for vulnerabilities.
It does not require access to the source code.
Low false positives: According to OWASP's benchmark project, DAST solutions produce fewer false positives than other testing approaches.
Identifies configuration issues: DAST excels at finding security vulnerabilities that occur only when the application is operational. In addition, DAST attacks an application from the outside in, placing it in the perfect position to find configuration mistakes missed by other AST tools.
Logic vulnerabilities: These flaws are hard to detect early in development. These issues are caused by security configurations, data, and other things, making them hard to detect in non-production environments. Most bug bounty programs pay for these kinds of flaws instead for traditional and low-hanging issues. Detecting these flaws requires you to write test cases and execute them continuously in dev/production.

Cons of DAST
Does not find the exact location of a vulnerability in the code
Tests can be time-consuming.

Here are a few free DAST solutions you can run safely against your live applications:

EthicalCheck:
Free & Automated DAST for APIs.
https://apisec-inc.github.io/pentest/

Burp Suite
Write your tests
https://portswigger.net/burp/communitydownload