ServerInfo

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This nifty little program allows you to monitor a server or servers; auto-connect when a public slot is free, a player connects, etc; alert you when a player connects; and search WON like GameSpy. I like this program because it is much cleaner and uncluttered than all the other ones I've seen out there. :)
Refunct the Defunct

40Kb, 226 downloads
This will fix your function keys. (F1 and F2)
Simple-Script for Natural Selection

115Kb, 592 downloads
This is a script pack that will simplify your gaming experience. It contains one-touch radio commands for Marines and drop/build ones for the Commander. These will over-write your "F" keys, and spacebar will be crouch-jump. I really haven't found much use for scripts with the Alien side other than the crouch-jump that enables you to blink by jump-clicking, so there are none.
Half-Life IP Launcher

354Kb, 279 downloads
This neat little program allows you to connect to a server using its IP number. Just select the MOD and punch in the IP number. It works with passwords as well.
Pak Explorer

170Kb, 518 downloads
Explore your Halflife .pak files with this neat little program. Pak filfes contain sounds, models, sprites and stuff. They are in your half-life/valve folder. (pak0.pak, pak1.pak)
UO Trace

39Kb, 211 downloads
A nice traceroute utility originally used for Ultima Online servers, but can be used for anything...like NS servers. :)