The following table provides a comparison of different client & server implementations:
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Name | Language | Role(s) | Negotiation(s) | Protocol id(s) |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| http4s-blaze | Scala | server | ALPN | h2, h2-14 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| cl-http2-protocol | Common Lisp | client, server | NPN, direct | h2-14 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Deuterium | C | client, server | ALPN, direct | h2, h2-14, h2c, h2c-14 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| F5 | C | server, proxy | ALPN, NPN | h2-14 (11.6.0 HF2) h2 (upcoming release) |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| H2O | C | Server, proxy | ALPN, NPN, Upgrade, direct | h2, h2-14, h2-16 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| http-2 | Ruby | server, client | ALPN, NPN, Upgrade, direct | h2, h2c, h2-17 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| http2 | Go | client, server | NPN (+ ALPN w/ Go 1.4) | |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Jetty | Java | client, intermediary, server | ALPN, Upgrade, Direct | h2, h2-17, h2-14, h2c, h2c-17 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| LiteSpeed Enterprise | C++ | Server | ALPN, NPN, Upgrade | h2, h2-17, h2-14, h2c |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Lucid | Erlang | Server | NPN, direct | h2, h2-16, h2-14 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Microsoft | C/C++ | Client, Server | ALPN | h2 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| mod_h2 | C | Server | ALPN, NPN, Upgrade, direct | h2, h2c (plus -14,-16) |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Netty | Java | client, server | ALPN, NPN, Upgrade, direct | h2, h2c |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| nghttp2 | C | client, server, intermediary | ALPN, NPN, Upgrade, direct | h2, h2-16, h2-14, h2c |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| node-http2 | NodeJS | server, client | ALPN, NPN, direct | h2 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| OkHttp | Android, Java | mock server, client | ALPN, NPN | h2 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| OpenLiteSpeed | C++ | Server | ALPN, NPN, Upgrade | h2, h2-17 , h2-14, h2c |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Protocol::HTTP2 | Perl | server, client | ALPN, NPN, Upgrade, direct | h2, h2c |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Brocade SteelApp Traffic Manager (formerly Riverbed/Zeus TM) | C++ | Server | ALPN, NPN, Upgrade, direct | h2, h2c |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Sasazka | NodeJS | server | NPN | |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| second-transfer | Haskell | server | ALPN | h2-14, h2 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Trusterd | C/mruby | client, server | ALPN, NPN, direct | |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Twitter | C++ | server, client | ALPN, NPN | h2 |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Undertow | Java | Server, Intermediary | ALPN, Upgrade | |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
| Warp | Haskell | Server | ALPN, direct | |
+--------------------------------------------------------------+----------------+------------------------------+----------------------------+------------------------------------------+
Links to products since I don't know how to keep table format with links inside.
This answer sounds reasonable, but it would be even better with citations. Can you link to any official documents supporting the claims made in this answer? – a CVn – 2015-06-13T13:02:49.227
@MichaelKjörling - No, I don't know about any official statement about this. I wish I would. My answer is based on personal experience. – Peter Hahndorf – 2015-06-13T13:08:09.980
So basically it's a great feature but will be of no benefit until mid 2016 at the earliest, for most of us with commercial applications could well be five years down the road! Thank you for your answer. Can't up-vote as my other Stack Exchange points don't count on this site :-( – gchq – 2015-06-13T18:14:28.230
1http://blogs.iis.net/davidso/http2 – Josh Robinson – 2015-12-03T15:15:42.037