Maybe you wish to keep skillset of internal staff within certain frame, while outsourcing selected technologies to external teams. Or you simply wish to acquire efficient engineers, within your budget limits. In any case, you keep your management, you organize sprints. Look & Feel is that you get extension of your teams, managed by your senior staff. Recommended languages/frameworks: Java, Python, C#, JavaScript (Node.js, React), Angular. Do not limit yourself to software engineers; you can expand your QA team as well, or team of consultants for solutions of major vendors