pngcrush is an excellent batch-mode compression utility for PNG images. Depending on the application that created the original PNGs, it can improve the file size anywhere from a few percent to 40% or more (completely losslessly). The utility also allows specified PNG chunks (e.g. text comments) to be inserted or deleted, and it can fix incorrect gamma info written by Photoshop 5.0 as well as the erroneous iCCP chunk written by Photoshop 5.5.
Poezio is a console-based client for XMPP, the protocol on which the Jabber IM network is built. Its goal is to let you connect to the network very easily (without having to create an account) and join various chatrooms immediately. It tries to look like the most famous IRC clients (such as weechat and irssi). Many commands are identical and you won't be lost if you already know these clients. Configuration can be done in a configuration file or directly from the client. It embodies the light, fast, geeky, and anonymous spirit of IRC while using a new, powerful, standard, and open protocol.
rgxg (ReGular eXpression Generator) is a C library and a command-line tool that generate (extended) regular expressions. It can be useful for generating expressions that match, for example, a specific number range (e.g. 0 to 31 or 00 to FF) or all addresses in a CIDR block (e.g. 192.168.0.0/24 or 2001:db8:aaaa::/64).
This is a simple command-line utilitiy to convert images from TIFF to PNG format. It is primarily useful in dealing with TIFF images that contain alpha channels (transparency information), since the NetPBM suite is (currently) ill-suited for such conversions. A few test images are included.