The code for both the client and server are open source (https://github.com/hypothesis/h) so this is possible. The server is designed to support the needs of large scale deployments, so this does come with some complexity compared to a system you would design for smaller scale usage.
The text on https://web.hypothes.is/ mostly targets schools and universities, because Hypothesis pays for itself by selling integrations with online learning platforms (Canvas, D2L, Blackboard etc.) and associated support.
The code for both the client and server are open source (https://github.com/hypothesis/h) so this is possible. The server is designed to support the needs of large scale deployments, so this does come with some complexity compared to a system you would design for smaller scale usage.
The text on https://web.hypothes.is/ mostly targets schools and universities, because Hypothesis pays for itself by selling integrations with online learning platforms (Canvas, D2L, Blackboard etc.) and associated support.