TEI Tite is a constrained customization of TEI designed for use when outsourcing production of TEI documents to vendors (who use some combination of OCR and keyboarding). While the canonical version is maintained by the Council, a derived version is used in the AccessTEI program.
Its most drastic departure from the TEI model is its lack of header. Its designers felt that Tite would be a format used only in a transitional state between delivery from an encoding vendor and conversion into a more suitable TEI format for archiving (perhaps using OxGarage, the web-based front end to Sebastian's stylesheets. That is, vendors would generally not create header metadata for encoded texts but would instead identify the texts for encoding and communicate with the customer about them using a unique identifier agreed upon by the two parties.
TEI Tite is not meant as a successor to TEI Lite. While both formats are limited subsets of the TEI and have seen adoption in libraries, they are designed for different purposes.
Schemas and documentation for TEI Tite and all other 'standard' customisations of the TEI are available at http://www.tei-c.org/Guidelines/Customization/ . See TEI @ SourceForge for bugs and feature requests relating to Tite.