You probably want "ActiveCampus Locator + WTD, SH3/ARM", "ActiveCampus Locator XP installer", or "ActiveCampus Locator source" (for Linux, XP, OS/X), depending on your platform.
WTD is from the RAMP group at UCSD and is used to collect network topology data for things like researching peer-to-peer routing. It's also used by the PDA locators for autoupdates so you don't have to keep coming back here and installing new locators. Do Science (capital 'S') a favor and use the WTD bundle, unless you're not comfortable with WTD's anonymous collection of topology data.
PDA locators with WTD:
ActiveCampus Locator + WTD, SH3/ARM, 1.0 (10/1/2002) (PocketPC ActiveSync install)
PDA locators without WTD:
ActiveCampus Locator, SH3/ARM, 1.0 (10/1/2002) (PocketPC ActiveSync install)
ActiveCampus Locator source (Linux, XP, OS/X), 1.0.0 (4/11/2003)