The official Matrix Identity Server implementation
sydent is an implementation of the Matrix Identity Server API in Python, supporting:
Instances currently run at matrix.org and vector.im; meanwhile others are free to run their own but they will not be able to participate in the global directory lookup table.
N.B. use of the Identity Server API is strictly optional in Matrix - it's only used to resolve 3PIDs to MXIDs.
Get the code from GitHub
Alternatively, slipeer maintains a fork with LDAP lookup.