for PC Software

CommView is a robust packet sniffing/network analysis program. It captures all activity on any port and offers an excellent filtering mechansim for weeding out the data you're really interested

Spytech's SpamAgent quickly and easily helps you stop spam from clogging your inbox with advanced rule-based and list-based filtering. Unusually it also provides facilities for fighting back against sources of spam

Diff'n'Merge provides quick and easy file and folder comparison with intelligent merging capabilities

FTP Right is a well-featured FTP client that lets you update a Web site with a single mouse click and resume interrupted downloads or uploads

HCML's Tardis is an advanced NTP client/server which can be used to synchronise one PC or an entire network. It supports internet-based Atomic Clocks, networked timeservers, GPS, Radio clocks, and more....

Alternatively if you can't stretch to twelve quid(!) there's K9 a lightweight client-only version