PSGI and Plack provide a common interface (PSGI) and shared infrastructure (Plack) for building web applications and frameworks in Perl. PSGI defines a standard way for applications to communicate with web servers through a request/response interface. Plack provides many server implementations like FastCGI and standalone that can run PSGI applications. It also includes middleware, testing tools, and utilities to help developers. This new approach allows frameworks and applications to focus on their logic while reusing common plumbing through PSGI and Plack.