1. "Coffee Pots," as made famous by the Rev. W. Awdry:
These VERY early locomotives were built with a vertical boiler, which eliminated the need for boiler tubes because the water was always resting atop the firebox. No significant reliability problems were recorded, except when the Best Friend of Charleston's fireman closed the safety valve, resulting in a boiler explosion. This idea was abandoned largely because any larger locomotives would be completely impractical.
2. Erie's Camelback Mallet
Before the new firebox for anthracite was designed, the Erie found itself lack in power. So, it put together two good ideas, and voila!
3. Ludlow & Southern's Steam-Turned-Diesel 4-6-0
So, your ten wheeler got in a wreck, and you don't want to spend a lot of money to replace it. Got some spare part slying around?
4. Miscellaneous Rebuilt Diesels
Sometimes, the generic Geep just isn't good enough for your tough and unique locale. Take it in your shops and personalise the ol' gal!
5. Irish Monorail
Listowell and Ballybunion ran these in revenue once, but they were discontinued because the racks acted as fences and were a general public nuisance. And yet, now they run again as a tourist railway!
I'm editing the original post now to add more.
