Hgfs is a read-only filesystem interface to Mercurial repositories. The interface gives access to the commit message, manifest, and files of each revision, and to .tgz's of each revision (the .tgz's are generated as they are read). The filesystem is a front-end for the Mercurial library that comes with it. All code is written in Limbo, for Inferno.
Httpd is a modern httpd for Inferno. It supports HTTP/1.0 and HTTP/1.1, virtual hosting, CGI and SCGI, logging, index file serving for directories, and directory listings, has configurable MIME types, understands range and conditional requests, does HTTP Basic authentication, and supports redirections based on regular expressions.
Memventi is a Venti daemon. It speaks the same Venti protocol as the real Venti in Plan 9 from Bell Labs. It is a storage server that stores data blocks up to 56KB using its SHA-1 hash (called its score) to address it. It keeps a mapping of score to disk location in memory (in a memory-efficient manner). Blocks written cannot be removed, and blocks are only written once. Memventi writes new blocks to an append-only file, thereby making file corruption due to bugs practically impossible.
xz is a data compression program using the LZMA algorithm and a similar user interface to gzip. Typically it compresses both tighter and faster than bzip2, and decompresses nearly as fast as gzip. The .xz file format includes headers and checksums, and also includes data filters (LZMA2) that can increase compression further.