Is Atlas open source?

Could you please clarify for me if Atlas is indeed an open-source project? It's important to understand the transparency and accessibility of its codebase, as this can significantly impact its security, development potential, and community involvement. Additionally, knowing if it's open source would allow users to contribute to its improvement and audit its code for potential vulnerabilities. Could you elaborate on the status of Atlas's source code and whether or not it's accessible to the public?