Finally, I rejoined the ntppool.org project again. Several years ago, I already contributed with several Stratum 1 systems which were connected to a Stratum 0 (GPS). Nowadays, most ones do not care about NTP and time synchronization anymore but it gets more important than ever when it comes to encryption, authentication and logging. Therefore, I took my old Stratum 0 GPS systems and created four new ntp server which are also included within the nto pool project. But of course, you are also able to use them directly without using the pool.
ntp01.gyptazy.ch (stratum 1)
IPv4: 37.114.42.55
IPv6: 2a00:ccc1:102:24c::1337
Location: Frankfurt, Germany
ntp02.gyptazy.ch (stratum 1)
IPv4: 37.114.55.6
IPv6: 2a00:ccc1:102:26c::1337
Location: Frankfurt, Germany
ntp03.gyptazy.ch (stratum 1)
IPv4: 45.129.181.241
IPv6: 2a03:4000:47:1f1::1337
Location: Nürnberg, Germany
ntp04.gyptazy.ch (stratum 1)
IPv4: 45.157.178.14
IPv6: 2a03:4000:4b:6e::1337
Location: Nürnberg, Germany
You can also find some further stats here.