Is Vagrant an alternative to Docker?

Vagrant and Docker can be alternatives in some scenarios but serve different purposes and are often used together. Vagrant builds and manages these virtualized environments, it utilizes full VMs through providers like VirtualBox, making Vagrant perfect for cloning complete development environments on local machines.
Docker uses lightweight containers, not full VMs, and allows applications to run on resources with minimal overhead in isolated environments. Docker is better fit for application deployment in microservices architecture and scenarios where scalability and fast startup time are needed.
Vagrant and Docker could sometimes be used interchangeably for local development, the lightweight containerization of Docker makes it much more versatile for a wide range of scenarios with respect to building, testing, and deployment in DevOps workflows.