There are a couple of other Modders who created custom tracks for FO2 who would hopefully make new tracks for FOUC but it takes a lot of work and testing to get it right.
Like Purple44 said, FOUC wasn't a big seller at the time but has sold a lot of copies recently via Steam that I can race on-lone every night now. What a comeback!
The game was falsely claimed to be "FO2 on Steroids". There is a lot more to it that makes it better than FO2 IMO. Sadly there was not anyone willing to make a filter to import the cars into a 3D program like "Zmoldeler2, thanks Oleg!" and the dreaded Games For Windows Live that really drove people away from the game.
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Purple44 explains it the best:
The problem with Microsoft's GFWL is it divide the online racing community!! If you do not live in one of the supported countries ( only 26 supported countries at the time DIRT 2 got release ), you will be block from racing online. Unless you know the trick to lie when you first set up an GFWL online profile from an unsupported country.
When DIRT 2 ( Codemasters first GFWL game )went up for pre-order on Steam, there was no warning about GFWL and the unsupported country issue and it took Codemasters 2 month after release of DIRT 2 before Steam DIRT page got updated with this information.
By then a lot players got screw over ( block form racing DIRT 2 online ) by GFWL!
"Don't feel right buying DIRT 2 if others are getting screwed out of their hard earn dollars." GFWL stole my game Codemasters has finally seen the
light and has stop using GFWL!!!! Now I can buy GRID 2 when it come out next year.

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I have uploaded a couple of Track Mods for FOUC, you might enjoy them.
FlatOut Ultimate Carnage Dirt to Asphalt and
FlatOut Ultimate Carnage FreeRoam Mod by Heddly