xtee (cross-tee/expanded tee) is a program for building complex pipelines. It resembles the tee command, except that instead of copying stdin to stdout, it copies an input file to stdout and stdin to an output file. You can use xtee for building things like a bidirectional HTTP filter (using netcat and sed).
log2rotate is designed for rotating backups with an optimal balance between retention and space usage. Instead of rotating backups using some fixed period such as daily, weekly, monthly, or yearly, it rotates backups using exponentially-growing periods. The exponential periods are based on the base 2 logarithm or squaring, depending on how you look at it.
Re: nifty tool, but a slightly misleading description
Thanks for pointing out that that part needs clarification. I'll make an edit.