TinyOWS is a lightweight and fast implementation of the OGC WFS-T specification. Web Feature Service (WFS) allows to query and to retrieve features. The transactional profile (WFS-T) allows then to insert, update or delete such features.
From a technical point of view WFS-T is a Web Service API in front of a spatial database. TinyOWS is deeply tied to PostgreSQL/PostGIS.
TinyOWS is safely used in quite big GIS infrastructures, for instance, to allow European farmers to report the locations and crops on their fields (and then to be paid by EEC accordingly).
TinyOWS strictly implements OGC standards and successfully passes all WFS OGC CITE tests (and even beta ones).
TinyOWS is part of the MapServer Suite, but provided as a distinct module (i.e you could use it in conjonction with MapServer and MapCache, or as a standalone app) But both MapServer and TinyOWS could use the same configuration file, if you want to (or native TinyOWS XML config file).
OGC's WFS homepage