IMHO Octodad is the one most worth checking out from when I looked the other day. It makes me want to play the full/updated version just to see how far it got from initial concept.

<span class="bold">Serafina's Saga</span>

Young Serafina has spent her entire life alone in the jungle with only her guardian, a mysterious man named Arken, as company. When Arken is captured by a group of soldiers and carried away, Serafina must venture outside the forest to save him. On her journey to the heart of the kingdom, Serafina discovers a whole new world beyond the shadows of the jungle. She will also learn the dark truth of Arken's past and thus her own. How she chooses to use this knowledge will change the fate of the entire kingdom.

<span class="bold">A Fragment of Her</span>

An interactive short story made for the Point & Click Jam 2014, following Selina, an aspiring art student, as she starts her studies at the University of Applied Art right after moving to the big city.


<span class="bold">Being Her Darkest Friend</span>

“Being Her Darkest Friend” is the successor of “A Fragment of Her” and was made for #AdventureJam in April 2015.


<span class="bold">Late Last Nite</span>

Welcome to Late Last Nite, an adventure in excess.

Join our protagonist Morgan as she stumbles through a series of bizarre fantasy settings -- a mer-pirate lagoon, a junk food forest, and a steampunk vampire nightclub -- in search of three missing relics. How will her night end? It's up to you to decide!

<span class="bold">I Hate Candy</span>

There's no time to explain!
Our fellow scientists is trapped on the planet that made of candy!
Hurry up and rescue them!
The ship is in distress with scientists on a strange planet, consisting of sweets.
The locals are happy to show newcomers and friendliness, throwing those sweets.
You receive a distress signal from the scientists and goes on a rescue mission.
Since sweets shield the signals from the beacons of the victims, their exact location can not be found - so the mission entrusted to you to come down to the planet to get the unlucky scientists.
And this operation would be a walk in the park on a sunny day, if it were not for one thing!
Representatives of the race of the hero can not stand sweet ...

<span class="bold">The Terrible Old Man</span>

This is a short interactive adaptation of the H.P. Lovecraft short story of the same name.

Story:

Three men of loose virtue are enjoying a drink in a local tavern, when they overhear the story of a rich and feeble old man who lives in town. They soon plot to take his treasures...

Features:

- An adaptation of the classic H.P. Lovecraft short story
- Beautiful hand drawn graphics and animation by John 'Barracuda' Inch
- Fully animated cut scenes
- A cast of several characters
- 640 x 400 resolution
- Point and click interface
- Inventory items
- Horror!

<span class="bold">Bullet Bubby</span>

Bullet Bubby is a "shoot em up" or alternatively a "bullet hell" type of game. The game centers around boss battles, to an extent were there are no levels! Instead you must go head to head with huge and powerful bosses who employ the age old tactic of "shoot at him until he is dead".

Bullet Bubby features:

An unique and interesting artstyle

An insane and twisting story.

Over 7 tricky and difficult bosses

An upbeat music track that is sure to get you pumped for action


<span class="bold">Round Battle</span>

A new, funny and free 3D shooter game for your smartphone! Use your fingers to destroy your opponent, in a lot of 3D environments, with a bunch of weapons and using your skill!

Fight your battle in the arena and try to push down your enemy with kicks or bombs! Dodge, jump and shoot in this free top down shooter with cute 3D isometric graphic. Follow the learnings of your wise master and get to the top of the world tournament of Round Battle, where there aren't rules!

Take advantage of the 3D arena to surprise your opponent: hidden passages, random events, switches and much more, but be careful, your competitors can be really hard to defeat!
To help you in battle you can use everything you'll find: bombs, mines, shotguns, lasers and much more weapons and power-ups!

You can also upgrade yourself to make the battle easier, like in every shooter game: change your character, put on your favourite hat

FreeOrion

FreeOrion is a Master of Orion inspired game. I saw people mentioning a possible MOO remake, so I remembered seeing this before.

As far as I see, it's a turn based space conquest simulation. I compared the looks of MOO with FreeOrion and similarity is obvious, but I haven't really played any of them (unfortunately not a fun of space conquest type of games) so I'm not sure how similar the gameplay is. Although you might check it out and write up your impressions.

Videos:
https://www.youtube.com/playlist?list=PLFG-jNjCiKSNli1Tn0mNcq5t_Q4skPK5K,
https://www.youtube.com/watch?v=NhZawhGK8BU

Pics: http://www.freeorion.org/index.php/Screenshots

Have fun. :)

Edit: Forgot to say it's free and open source. Binaries are available for Windows and Mac. For Linux check your distribution's repositories. If not there, search the 3rd party repositories.

I see OP asked to categorize games. FreeOrion is a Space Simulation and a (Space) Strategy. So if you are still around you can put it in any of those you feel it belongs. :)

I see Vulture is in the first few posts. Vulture went commercial. It's still open source, but the binaries are not provided anymore. The binaries are available on Steam.

If you have the links to the last free binaries (they were hosted on Dropbox), they seem to still work. If not, check the Internet Archive's Wayback Machine, but keep in mind they might not last long.

The source is available here:
http://download.darkarts.co.za/vulture/Vulture%20for%20NetHack%20-%20Community%20Edition%202.4.zip and on Bitbucket: https://bitbucket.org/clivecrous/vulture (might not be the most recent).

<span class="bold">Scimmiotto - Around The World</span>

Scimmiotto Around the World is a 3d platform created with unity 3d like crash bandicoot game or similar. Present the classic pickup static obstacles, enemies, world boss weapons and special abilities (super jump, super-velocity, immunity ):
Developed with a budget of $ 0 about 1 year of development.

The game consists of 14 levels + 1 Open world mode

14 levels are divided into 4 chapters :

- Forest - 3
- Desert - 3 ( +1 Underwater level )
- Space -3
- Alaska - 3
- Final cutscene level

These terms "Open World" (the monkey turns to a map of average size to search for 5 magical bananas and solve a simple quest ).
The game is quite optimized with graphics turned with colors on, almost cartoon, to ensure stable even at 30 fps for old pc.Even though all the graphics is perfectly suited to the gameplay making the game balanced.

Realism Invictus

A mod for Sid Meyer's Civilization IV that tries to make the game more realistic and historicaly accurate.

Citing the web site: Haven't tried it yet but it looks interesting. The armies in Civ are pretty much generic so a bit more realism might be interesting.

<span class="bold">Aborigenus</span>

Flying islands were a resident of stability for thousands years. Humans and animals lived in harmony. However, those days are gone. Animals became aggressive. Tribes are in war. And somewhere deep in caves ancient evil awakens.
Dark times are coming.

Aborigenus is a beautiful pixel-art rpg-platformer. Explore ancient forests, deep caves and hot deserts. Fight with different creatures and enemies. Develop your skills and abilities. Rescue your love and destroy evil.
You can save the world... if you want.

Great mod! Thanks for posting it! I think I'll have another go at Civ4.

It seems there are many good mods for Civ4.
I personally really liked the "" mod and the "[url=http://forums.civfanatics.com/forumdisplay.php?f=263]Fall from Heaven: Age of Ice" mod.

<span class="bold">SUPER SQUARE CHAOS</span>

Super Square Chaos is a highly addictive, fun and action packed platform game. The simplistic art style and the unique gameplay make for an enjoyable gaming experience for everyone of all ages. Jump, shoot, blow stuff up and dodge the bad guys as you collect all the crystals they drop to get to the next level. As you try to complete each level you will pick up a large variety of weapons that will randomly spawn. Blowing up the level sounds like a lot of fun, but be careful... These bad guys like to blow stuff up too!

Full game will be available featuring:
◆ 50 + Destructible Levels
◆ 12 Worlds
◆ 12 Unique boss fights
◆ A huge variety of weapons
◆ A large character selection

To be honest, haven't tried any. I barely play it unmodded. :) But thanx for the recommendations. I will have to check them out.