Open-source C implementation of the EPC (and 5G Core): MME/HSS/SGW/PGW for LTE. Paired with srsENB it provides the core network behind a test/rogue eNodeB so you can provision test subscribers and drive attach/authentication/identity NAS procedures end-to-end.
Lifecycle not assessed: nobody has checked yet whether this tool is still maintained, sold or working. Check the project's own page before relying on it.