As I have said in an earlier post, if you want to do game modding, stick with the PC. The reason being most of the construction sets (or toolkits) released by game publishers tended to be PC-based. Toolkit for Mac and Linux platforms is almost unheard of.

Moddable games such as the Neverwinter Nights series and the Elder Scrolls series (Morrowind & Oblivion) are inherently interesting to educators and researchers (like me) because these games have the potentials to be modded into something entirely different for use with a non-entertainment context, in an educational or training environment. In another word, they have potentials to be modded as “serious games.”

Examples of PC games with construction toolkit (i.e. with blessing from the publisher to mo, mod, and mod) include:

• Bioware published Neverwinter Nights (2002) and gave away the Aurora Toolset to the gamers community. Atari/Obsidian published Neverwinter Nights 2 (2006) and gave away the development toolkit. Both toolkits (NWN 1 & 2) are found on the game CD-/DVD-ROMs.
• Since Morrowind (TES: III, 2002) and Oblivion (TES: IV, 2006) are both from The Elder Scolls series of games, Bethesda called the toolkit The Elder Scroll (TES) Construction Set. You can find more information about The Elder Scrolls Construction Set here, and download the Construction Set here. (Note: the construction set for Oblivion is not backward compatible with the construction set for Morrowind.)
• THQ’s Titan Quest also provide the community with the Titan Quest construction toolset with the game CD-ROM. More information on modding TQ is available here.

Many gamer-created mods can be found on IGN’s Vault Hub. Check out the NWN2 Vault, and Titan Quest Vault.