EIGRP Implementation by Non-Cisco Vendors
EIGRP was originally a Cisco proprietary protocol. However, in 2013, Cisco opened up a limited version of EIGRP for implementation by other vendors. This limited version includes some features like High Availability but excludes certain other EIGRP features. The implementation details were published in RFC 7868, allowing other vendors to freely use and implement the protocol.
This submission of implementation details to the IETF was an attempt by Cisco to have parts of EIGRP become a standard, however, the full protocol has not been standardized and remains proprietary.
Even so, EIGRP is now supported by vendors other than Cisco, and their equipment can interconnect with Cisco devices using EIGRP. This move has increased the interoperability of EIGRP across different network equipment manufacturers, while still allowing Cisco to maintain some proprietary features of the protocol.