Your favorite hidden gems?

[G'th]

Every modding community always those hidden gem mods that are very obscure but just so very very awesome that its basically criminal they don't get more exposure, and I'm always searching for them no matter what game it is.

My favorite hidden gem for KSP right now is Starvision's Flag Decals mod, which I was able to re-purpose in order to make this possible:

There used to be a couple more but updates have long since broken them beyond my ability to repair.

So, what are your favorite hidden gems?

[Fail-Man 3D]

My favorite "hidden gem" isn't even a KSP mod; it's (still) unionfs, which I use to manage mods.

Manual mod management via "unzip" and "rm -rf" gets to be a bit of a chore with the number of mods I run (upwards of 120 at a time), and not all of my favorite mods are available through CKAN.

To make matters worse, different modders follow different directory-structure conventions for their release packages; ones I have seen include (but are not limited to):

• Put GameData and Ships into the root of the archive (I call this "canonical form", as it lets me do a simple "unzip ${pkgname}.zip -d ${modname}/" and call it finished)
  
• Put GameData and Ships into a directory named after the mod, then put that directory into the root of the archive.
  
• Put everything that goes into GameData into the root of the archive, but also put Ships/ in there, too.
  

unionfs lets me canonicalize the mod's directory structure once, then use it in multiple project-specific KSP prefixes without creating additional copies.

AIES Aerospace is a close second  it's not on my "must-have" list (as I have been forced to do without it for a long time), but the ultra-thin 1.25m decoupler, radial mini-RTG, and wonderful liquid-fuel engines were worth the wait for 1.04 compatibility.

[MrHappyFace]

I particularly liked the nyan cat that appeared in ModuleManager on April 1st.

Also liked KSI Placement Services: http://forum.kerbalspaceprogram.com/threads/123707

[Mad Rocket Scientist]

WASD Editor cam, no offset limits.

[komodo]

Vanguard parachutes. It still works with 1.0.x as far as I know. A little funky to install, but the ability to actually bail out of a potential fireball and float to the sweet sweet ground is hard to under state.

[Nansuchao]

Instell technologies, few engines for planes, but really wonderful.