List of free rfc3161 servers.

rfc3161.txt

https://rfc3161.ai.moda
https://rfc3161.ai.moda/adobe
https://rfc3161.ai.moda/microsoft
https://rfc3161.ai.moda/apple
https://rfc3161.ai.moda/any
http://rfc3161.ai.moda
http://timestamp.digicert.com
http://timestamp.globalsign.com/tsa/r6advanced1
http://rfc3161timestamp.globalsign.com/advanced
http://timestamp.sectigo.com
http://timestamp.apple.com/ts01
http://tsa.mesign.com
http://time.certum.pl
https://freetsa.org
http://tsa.startssl.com/rfc3161
http://dse200.ncipher.com/TSS/HttpTspServer
http://zeitstempel.dfn.de
https://ca.signfiles.com/tsa/get.aspx
http://services.globaltrustfinder.com/adss/tsa
https://tsp.iaik.tugraz.at/tsp/TspRequest
http://timestamp.entrust.net/TSS/RFC3161sha2TS
http://timestamp.acs.microsoft.com

@Manouchehri great, thanks a lot, works perfectly. Now we can call our "time stamper" util with your load balancer.

I created a simple time stamp query http(s) client and sent a simple query to the servers mentioned in your list. Here are the simplified results:
Probably some of these URLs need a path (e.g. freetsa.org should be http(s)://freetsa.org/tsr).

http://timestamp.globalsign.com/tsa/r6advanced1: OK
http://timestamp.digicert.com: OK
http://timestamp.acs.microsoft.com: OK 
http://time.certum.pl: OK
http://rfc3161timestamp.globalsign.com/advanced: OK

http://zeitstempel.dfn.de: fail
http://tsa.startssl.com/rfc3161: fail
http://tsa.mesign.com: fail
http://timestamp.sectigo.com: fail
http://timestamp.entrust.net/TSS/RFC3161sha2TS: fail
http://timestamp.apple.com/ts01: fail
https://tsp.iaik.tugraz.at/tsp/TspRequest: fail
https://rfc3161.ai.moda/microsoft: fail
https://rfc3161.ai.moda: fail 
https://rfc3161.ai.moda/apple: fail
https://rfc3161.ai.moda/any: fail
https://rfc3161.ai.moda/adobe: fail
https://freetsa.org: fail
http://services.globaltrustfinder.com/adss/tsa: fail
https://ca.signfiles.com/tsa/get.aspx: fail
http://rfc3161.ai.moda: fail
http://dse200.ncipher.com/TSS/HttpTspServer: fail

@HeikoSchlittermann Could you please explain how your client works? Those results seem very wrong to me.

The following have stopped working for years:
http://tsa.startssl.com/rfc3161
http://services.globaltrustfinder.com/adss/tsa
http://dse200.ncipher.com/TSS/HttpTspServer

The following, as mentioned, had the URL wrong:
https://freetsa.org it should be: https://freetsa.org/tsr

The rest is working properly.
So something is wrong with thou simple time stamp client.

rfc3161 timestamping servers – March 2025 update

[#] = LTV (long-term validity) enabled
[*] = increased sigvalue size; if using Adobe Acrobat on Windows, a registry modification may be required in accordance with these instructions

Working

QUALIFIED (EU Trust List)

http://tss.accv.es:8318/tsa [#]
https://timestamp.aped.gov.gr/qtss [*]
http://tsa.baltstamp.lt [#]
http://tsa.belgium.be/connect [#]
http://ts.cartaodecidadao.pt/tsa/server [LTV]
http://ts.quovadisglobal.com/eu [# *]
http://tsa.izenpe.com [#]
http://timestamp.sectigo.com/qualified

TRUSTED (Adobe Trust List)

http://rfc3161.ai.moda (and other URL variants) [*]
http://timestamp.digicert.com
http://timestamp.comodoca.com (and other URL variants) [*]
http://timestamp.entrust.net/TSS/RFC3161sha2TS
http://timestamp.identrust.com
http://ts.quovadisglobal.com/ch [*]
http://timestamp.sectigo.com
http://ts.ssl.com
http://tsa.swisssign.net [*]
https://tsa.wotrus.com

UNTRUSTED

http://timestamp.apple.com/ts01
http://time.certum.pl [*]
https://tsa.cesnet.cz:3162/tsa
http(s)://zeitstempel.dfn.de [*]
http://tsa.sinpe.fi.cr/tsaHttp/ (trailing slash required)
http://timestamp.globalsign.com/advanced (and other URL variants)
https://freetsa.org/tsr
http://tsa.lex-persona.com/tsa
https://tsa.mahidol.ac.th/tsa/get.aspx
https://time.mconnect.mc
http://timestamp.acs.microsoft.com
http://dss.nowina.lu/pki-factory/tsa/good-tsa
http://timestamp.ssl.trustwave.com

Not working

http://psis.catcert.cat/psis/catcert/tsp (timeout)
http://tsa.mesign.com (timeout/crash, likely moved to https://tsa.wotrus.com)
http://tsa.safecreative.org (timeout/crash)
http://tsa.sep.bg (timeout/gone)
http://sha256timestamp.ws.symantec.com/sha256/timestamp (timeout/error)
https://tsp.iaik.tugraz.at/tsp/TspRequest (error)