So, I had this idea about how to get a working cloaking device in FSO. I started working on it and got pretty close to finished when I learned that this idea had already been explored at least once.. but I figured I'd post it anyway...
Anyhow, I used the change-ship-class sexp and created some ship variations and just swapped between them upon the keypress. I also added a hud element to tell you the status of your cloak. Once I got the basics working, I decided to test it on some Maras. I set it up so that when cloaked they would ignore the player UNLESS the player has fired a weapon within the last 15 seconds. Also, with the cloak on, you don't have shields or afterburners... (That + my horrid piloting skills and the fact that I didn't realize the shield bug at first caused me to not do so hot in this preview video.) Also, I cut out the latter half of the mission test because I figured you guys didn't really want to watch 12 minutes of me shooting Maras...

Anyhow, I fixed the shield thing and am uploading a small modpack so you can rummage through it and see how I pulled it off.
Lastly, I was more interested in seeing if the idea would work so the actual cloaking effect is sub-par at best, IMO. Were I to actually use this in a campaign, I would make a cooler effect.
here's the Youtube video.Here's the link to the modpack.EDIT: In retrospect, I might see what I can do about the engine flares dissapearing... And I would consider a texture trick to distort the cloaked ship rather than have it purely invisible.
EDIT2: I forgot to unflag 'invulnerable' for Alpha 1 when I zipped this up. I'll upload a new version soon.