Alrighty, I just added the Exile series games to the list, and also the following MVP Software-owned titles:

Adventure

• Robomaze III [download]

Platform Game

• Robomaze II: The Lobby [download]

Turn-Based Tactics

• Rapid Response [download]

Just found this really huge blog dedicated to liberated games:
http://juegosliberados.blogspot.com/

It's in either Spanish or Portuguese (can't tell because I'm not very familiar with both languages), but everything is pretty self-explanatory. The blog seems to feature quite a few really obscure games too.

I figured the blog is in Spanish (since it has links to Spanish Wikipedia). Here's some of the interesting games from the database that caught my attention:

• Tecno - The Base - a futuristic FPS made in the early 2000s style, although apparently it was released much later than that.
• PaybackTime 2 - an obvious X-COM clone, which was distributed as shareware in the nineties (here's their home page from back then), released for free in 2011.
• Cosmos Quest series, obviously inspired by Sierra's Space Quest games.
• StarFight series shmups.
• A huge number of games produced by the German developer Motelsoft, ranging from Amiga and DOS adventure and RPG games to Windows FPS titles.

Added SideLine to the list.

Meanwhile I put together a small list of liberated PC games (with a handful of non-PC titles) as an OpenDocument spreadsheet. The list can be sorted by platform, year of release, genre, original distribution model, source code license (if available), programming language, engine, and includes working download links. A separate page lists the sources that I used when compiling the list.

The games I omitted from the list are temporary Sierra giveaways from the early 2000s, Cinemaware and Rockstar games (I think in both cases these are no longer freeware in any form), and multiplayer-only titles. Also, apart from directly liberated games I've included a small numbers of unofficial conversions and remakes that have been retroactively authorised by game owners, in the absence of the respective original games being freeware. There are over 400 games on the list.