libh2o is a library, h2o is a full fledged webserver using libh2o. They are both made by the same people and released together. Having all the core features in

libh2o is a library, h2o is a full fledged webserver using libh2o. They are both made by the same people and released together. Having all the core features in a library allow any developer to use libh2o to easily add a webserver to their program. note: this is explained in the first part of the link.