I am watching Maptool develop with interest, it has come a long way and Mando is right it does a lot for no cost. Another low cost one with better character tracking but worse map features is OpenRPG+. I think both of these are perfectly functional and best of all free.
Maptool is most similar to Battlegrounds for the commercial ones. Both have maps and chat but don't record character info. If you want maps tokens and chat with less overhead then these are good programs.
OpenRPG+ is most like FG or kLoOge which base things off of a character sheet. FG is a good product with a very nice interface, and with some customization could be very fun for use with HARP. At about the same price or a little cheaper is kLoOge Werks which is what I have been using for HARP for some time.
kLoOge has full customization for HARP, several HARP GM's got together and customized the heck out of it. We built custom character sheets, stock monsters, macros and utilities (like treasure generators) and even shared some adventures. Most recently I upgraded the HARP character sheet to export directly to kLoOge XML so you can generate characters and NPCs and export them to kLoOge with minimal work.
http://www.ironcrown.com/ICEforums/index.php?action=tpmod;dl=item565The kLoOge HARP version (yes there is an SF version in testing if anyone wants a copy) tracks time in harp format with calendars for Cyradon, EoH and Shadow world. It tracks initiative according to HARP rules. It tracks hits, stuns, bleeding, etc.. and it will automatically adjust rolls based on the range of the weapon. There are custom buttons for applying criticals to tokens in ML like shorthand... plus a round maintenance button that adjusts hits for bleeding each round... and makes sure that stun rounds are calculated properly. This makes our online combat faster than I can manage FtF plus no bookkeeping on my part.
Of course there are other customizations and features that we came up with... The nice thing about kLoOge is it's adaptability to non d20 systems... heck I even play tested the battle master min rules with my group using this way back when to give Tim some feedback. A basic definition file is in downloads, and I can share some stock monsters and what not that we have come up with to anyone who is interested.
http://www.ironcrown.com/ICEforums/index.php?action=tpmod;dl=item487http://24.72.114.123/dgt/index.php?option=com_docman&task=cat_view&gid=14&Itemid=28To the main topic... Ah... I am waiting to spend a bunch of money on HARP print materials starting with a SF hardcover. And I have no intention of going to 4e... I prefer the BFRP/Rules Cyclopedia versions to current or future ones... the feat character build of modern ones is a nightmare that keeps getting worse.