Strata Source
The 
Strata, formerly known as "Chaos Engine", is a third-party Source engine branch using licenced code. It is a modified version of the CS:GO engine branch that combines the features of both CS:GO and the Portal 2 engine branch, along with many improvements that bring Source close to modern standards. This engine branch is still in active development.
Features
Feature list from Strata's Wiki
New since 
CS:GO engine branch:
- Native DirectX 11 renderer
- Support for DX11 by default
- DXVK support on Linux for both DirectX 9 and 11
- 64-bit support
- Support for 64-bit. 32-bit has been dropped
- PBR shading
- Uses shaders to attempt to more accurately simulate real-world light
- Ported
Portal 2 engine branch features - Including but not limited to World Portals and Portal gun
- Backwards compatibility with BSP v19-20, as well as native BSP v21 support
- Backwards compatibiltiy with TF2/HL2 branch models
Source 2013 uses a different model format, now supported- .webm video support, replacing older Bink videos
- Increased framerate, lower file sizes, and easier to author
- Many improvements to Linux support
- Fully cross platform engine tools and utils
- Steam Audio
- Many improvements to the Hammer level editor
- Many code quality improvements (Refactors, cleanup and C++20)
- Sentry crash report integration
Availability
Portal 2: Community Edition
Portal 2: Community Edition is a mod of Portal 2 that is intended to function as a base for community mods. The Portal 2: Community Edition team (abbreviated as P2CE team) consists of:
- Agrimar (programmer)
- Aly November (Artist, Level Designer, Modeller, Texture Artist)
- Andy (Level Designer)
- Baguettery (Artist, Level Designer, Media Designer, UI/UX Designer, Web Development)
- Craftablescience (Department Head, Programmer)
- Darvil (UI/UX Designer, Web Development)
- Erin (Department Head, UI Developer, Programmer)
- Ferni (Level Designer, Media Designer)
- Frosti (Level Designer, Modeller, Texture Artist)
- HankyMueller (Puzzle Designer)
- HugoBDesigner (Puzzle Designer)
- JJl77 (Department Head, Programmer)
- JoLoZ (UI/UX Designer, Web Development)
- LauraWebDev (UI/UX Designer, Web Development)
- leops (Programmer)
- Luke18033 (Level Designer, UI/UX Designer)
- Mystical Λce (Department Head, Level Designer, Public Relations)
- Obsolete (Level Designer)
- Orinji Neko (Composer)
- Ostojλ (UI/UX Designer)
- Ozxybox (Programmer)
- pivotman319 (Quality Assurance)
- Smaed (Programmer)
Momentum Mod
Momentum Mod is a standalone game focused on the movement gamemodes of all Source games. The Momentum team consists of: Template:ModernTodo
Portal: Revolution
Portal: Revolution is a mod of Portal 2: Community Edition that focuses on the area of time in-between Portal and Portal 2.
Custom Content
Source code for this branch is not available, however Authoring Tools exist in each game provided in this list.