help.openstreetmap.org is one of the contact channels of the OpenStreetMap community. You can post OpenStreetMap-related questions and/or help answer them. The idea of it is to find the best-suited answer to a question that is likely of interest to many people. Read the help site FAQ page to get started.
The software is OSQA.
The running software instance is (apparently) available in an OSM git repo (see Why does this site require third party resources?).
The OSQA software is unmaintained. See https://github.com/openstreetmap/operations/issues/149 "Migrate help.openstreetmap.org from OSQA" - a pinned issue at openstreetmap/operations.
If no replacement/migration is found/made this could lead to removing the site without a replacement. What was seriously considered in the past, and may happen on its own if unmaintained website will break down for some reason.