Title pretty much says it all. I've looked around and can't find the answer. I'm working on a mod and want to make expansions to it once I get the framework into place. Is there something like TES4Gecko available for FO3?

I can't give any first hand knowledge, as I have never tried, but according to a pretty old post you can use the convert function of Gecko on Fallout as well.

Source:
http://www.thenexusforums.com/index.php?/topic/87808-any-tool-to-convert-esp-to-esm/

Whether it works or not, or whether it depends on certain versions, I have no clue. Still, if no one else gives you an answer it is a place to start, or you can always just give it a try. I'd back up everything just in case something undesired would happen though =D

Its simple. You use Fo3Edit (look for it on Fallout3Nexus.com). Open it and load up your mod. Then under the mod, open the first tree (the + next to your mods name) and click file header. Then on the right side of the screen (make sure the View tab is selected in the bottom right) right click in the column to the right of record flags and click Edit. If it asks, say Yes, I'm sure I want to edit. Then check the box next to ESM and say Ok. Then close and save your mod. Then change your mod name from MyMod.Esp to MyMod.Esm. If you cant see the .esp to edit it, you need to do this. In windows (this is on 7, I think its similiar on Vista and XP) if you open the control panel, then click Appearance and personalization, then Folder options. Click the View tab, and uncheck 'hide extensions for known file types'. Then you can change the extension from esp to esm and your done.

Thank you both! As it turns out, TES4Gecko does work for FO3 files. And the FO3Edit method works nicely, too.