The following is a list of popular 3D software packages used by modellers for creating content for Half-Life 1 and Half-Life 2/Source games and mods. There also follows a list of links to various plug-ins and scripts that may be needed to enabled SMD format support in these programs.

Some of these programs are free, some have trial versions and some are available at discounted prices for those who are students.

If you have an additions or updates to the list, please post them as a reply to this thread and I'll endevour to keep the first post up-to-date.

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3D Modelling software

Softimage Mod Tool v4 (Free)
Cut down version of Softimage's commercial product. The preferred tool for Source based modelling and animation. Free download, requires registration to activate the SMD export tool.
http://www.softimage.com/community/Mod/v4/

3D Studio Max (Commercial / Trial)
Commercial product but available discounted for registered students. 30 day trial version also available. Numerous plug-ins available for Half-Life and Source modelling.
http://www4.discreet.com/3dsmax/

G-Max (Free)
Cut-down version of 3D Studio Max 4.2 specifically for mod making. Requires special "game packs" for your chosen game, but some exporters and "hacks" available for working with Half-Life/Source files.
http://www4.discreet.com/gmax/

Maya (Commercial / Trial)
Commerical modelling package but free "Personal Learning Edition" available for non-commercial use. Some SMD exporters available.
http://www.alias.com/

Lightwave (Commercial)
Commerical modelling package, no trial available.
http://www.newtek.com/

Blender3D (Free / Open-Source)
Once commercial modelling program now available for free.
http://www.blender3d.org/

Milkshape3D (Low-Cost / Trial)
Low cost, easy to use simple modelling program. Supports Half-Life and Source, but doesn't offer vertex weighting.
http://www.milkshape3d.com/

Fragmotion (Low-Cost / Trial)
Low-cost animation tool, with support for Half-Life and Source file formats.
http://www.fragmosoft.com/



3D Modelling software plug-ins

3D Studio Max
HL2/Source SMD import/export plug-ins:
http://www.chaosincarnate.net/cannonfodder/cftools.htm

HL1 SMD exporter for Max 6:
http://articles.thewavelength.net/587/

HL1 SMD exporter for Max 4.2/5:
http://www.maxplugins.de/

HL1 SMD import/export (MaxScript)
http://pages.videotron.com/browser/

G-Max
HL1 SMD import (MaxScript)
http://pages.videotron.com/browser/

Maya
HL1 SMD export (Maya 4.0?):
http://www.fileplanet.com/dl/dl.asp?/planetquake/polycount/Tools/halflife/maya4exporter.zip

HL2 SMD export:
http://mitglied.lycos.de/prallvamp/

Lightwave
HL2 SMD export:
http://coding.web.surftown.se/lw2smd/

Blender3D
HL2 SMD import:
http://www.3d2toy.com/downloader.php?ID=47

HL2 SMD export:
http://asrc.pjohnsen.com/index.php?option=com_remository&Itemid=40&func=selectcat&cat=2