grml is a Debian-based Live-CD. It includes a collection of GNU/Linux software especially for users of texttools and system administrators. grml provides automatic hardware detection. You can use grml for example as a rescue system, for analyzing systems/networks or as a working environment. It is not necessary to install anything to a harddisk, you don't even need a harddisk to run it, unless you want to (use grml2hd for this). Due to on-the-fly decompression grml includes about 2.1 GiB of software and documentation on the CD.
Whereas grml provides about 2.1 GB of software on a 700 MB ISO, grml-small is a flavor with online ~58 MB ISO-size (~170 MB uncompressed). It does not provide a lot of software but the essential stuff for being a rescue system on a business card CD-ROM or a small USB device. You can use the Debian package management system to install software on the fly (assuming you have network access to a Debian mirror).