Some further examples of unusual locomotives and railcars.
1. A First Michelin Pneumatic-Tyred Railcar (Type No.9)
The 1973 Railway World Annual edited by Alan Williams contained an article by W.T. Thornwell entitled, “Forward from Steam,” which featured a number of different proposals for developing passenger and freight services in the 1930s. One of the experimental vehicles which could be seen on British rails was the Michelin Pneumatic-Tyred Railcar. A picture appears in the Railway World Annual © M.W. Earley [1: p81]
Whether these railcars were small is perhaps a moot point, their appearance was certainly unusual as far as the UK was concerned. As far as I can ascertain, the railcars were trialed at two different locations in the UK.
The GWR put one through its paces between Banbury and Wolverhampton. The LMS used the route between Bletchley and Oxford. Neither company was sufficiently impressed by the trials to order one of the units. It appears that the LMS did go on to trial other railcars as a result. 
The Commercial Motor Magazine carried an article about this railcar on 16th February 1932, entitled, ”The Michelin Railcar in England.”  The article is full of praise for the railcar and somewhat exaggerates its top speed at 92 mph. Perhaps that should have read kph?
There is an excellent discussion about this railcar on the Disused Stations Website (http://www.disused-stations.org.uk).  It is surprising that the railcar is featured on a page about Cambridge Station as it is very unlikely that it ever visited Cambridge. Nonetheless, the detail provided about the railcar is excellent.
2. Guinness Factory Narrow Gauge Locos and their Standard Gauge conversion vehicle.
I have written about these locomotives elsewhere.  A series of small locomotives were purchased to move a variety of goods and produce around the brewery site in Dublin. Once the decision had been taken to use a narrow gauge rail system across the St. James’s Gate site, the basic system was laid between 1873 and 1877 under the supervision of Samuel Geoghegan who joined the brewery engineering staff in 1872 at the age of 28 and rose to the position of Head Engineer in 1875. The track gauge was settled at 1ft 10in, the loading gauge was to have a headway of six feet and a maximum width of five feet, and the maximum gradient was to be not steeper than 1 in 40. 
Two years after construction of the line had started, the first of the narrow gauge locomotives was delivered. This was a small Sharp Stewart 0−4−0 saddle tank costing £445, with inside cylinders (unusual for a narrow gauge locomotive) and numbered ‘1’ in the narrow gauge locomotive stock. It weighed only about two tons and proved to be inadequate for the work. One problem encountered with it was maintenance of the motion, which, being very near the ground, was inaccessible whilst the locomotive was on the road. Later, as more engines appeared on the scene, No.1 was used only for hauling the visitors’ special passenger train, and it was eventually withdrawn from service in 1913. 
In the following year, 1876, two locomotives were obtained from Stephen Lewin, of Poole, Dorset, at a cost of £366 each; they carried numbers 2 and 3 and were named HOPS and MALT respectively.
These locomotives were geared and had large flywheels, similar to steam rollers. Weighing about five tons each they were more powerful than No.1, but repair costs were high, they damaged the track and were slow and troublesome in operation. 
1878 saw two new arrivals, Sharp Stewart 0−4−0 side tank engines weighing six tons each and having outside cylinders. As they survived until 1925, they must have had a certain measure of success. 
After this Geoghegan designed his own locomotives. These were also an 0−4−0 side tank engine with horizontally mounted cylinders. An IRS article says that the cylinders were ”situated above the marine-type boiler driving through a dummy crankshaft and vertical connecting rods, which in turn drove the wheels. Instead of the cylinders being bolted to the boiler, they were fixed to the frames which were carried the full height of the locomotive above the top of the boiler. The side tanks were also attached to the frames. Another novel feature was the independent spring frame which consisted of eight steel leaves in pairs, two pairs on each side of the locomotive and one pair each above and below the axleboxes. It was attached to the front and back stays, so that by removing the pins and connecting rods, and with the locomotive lifted, the spring frame could be wheeled out from beneath the locomotive to receive attention and maintenance. The general layout of these engines was one of accessibility for repair but with maximum protection from dirt.”  Geoghegan’s drawing is shown in the image above. 
Ellison, the author of the IRS article, says that a “prototype locomotive was built in 1882 by the Avonside Engine Company, of Bristol, at a cost of £848, and numbered ‘6’ in the locomotive stock, This was also the last of Guinness’s narrow gauge steam locomotives to be built in England, all others being built by William Spence, of the Cork Street Foundry and Engineering Works, in Dublin. This firm built locomotives 7 to 9 in 1887, 10 to 12 in 1891 and 13 to 15 in 1895. A further four, the largest single order for these engines, were turned out in 1902, whilst 20 and 21 were delivered in 1905. 22 entered traffic in 1912 and the last two finally appeared in 1921. No.6 was withdrawn in 1936 but all the others survived the Second World War and lasted until the introduction of diesel locomotives.” 
Thompson describes the first of these locos as being “rather odd-looking. To solve the dirt problem it had a heavy box-like frame with the two cylinders mounted on the top horizontally. Their valve gear drove vertical connecting rods which engaged the wheels below. The boiler was inside the “box” with the funnel barely visible. The side tanks were an integral part of the frame.” 
The Irish standard gauge lines on the St. James’s Gate site dated from the late 1870s or early 1880s. It connected the brewery with what was at the time known as Kingsbridge goods yard, and at its greatest extent possessed about two miles of track, out of the brewery’s one-time overall mileage of ten. Ellison says: “The line started at the loading and unloading banks and then ran out of the premises and along the public highway for about 500 yards to the goods yard. Compared with the narrow gauge lines, this section had a largely level route, as Kingsbridge yard and the lowest part of the brewery, where the line started, were much the same height above the river. This section of line along the public road was laid in granite setts, rather in the manner of a street tramway, right up to the time of closure. Probably unique in Ireland the rail used was of the centre-grooved type on which the wagons ran on their wheel flanges instead of their treads, whilst another notable feature was the unusual points necessary with this type of rail, wherein the whole rail was moved like a stub point.” 
Initially horses were used to convey wagons on the broad gauge, but from 1888, hauling and shunting was undertaken by narrow gauge locomotives mounted on unique vehicles called “haulage wagons”, another of Geoghegan’s inventions.
“The way in which the haulage wagons functioned was most interesting. A narrow gauge locomotive was lifted by an hydraulic hoist which stood astride a short section of gauntletted, dual gauge track. A haulage wagon was then propelled under the narrow gauge engine and the latter lowered between the frames of the former. Both ends of the locomotive were engaged in the wagon and the wheels of the narrow gauge engine rested on rollers whose shafts were geared to the running wheels of the haulage wagon at 3 to 1 reduction.” 
A view of a haulage wagon from above. On the left are the broad-gauge wheels, and in the centre is one of the rollers driven by the wheels of the narrow-gauge locomotive. Immediately to its right is the casing for the 3 to 1 reduction gears. The curved bit of metal at top right was presumably to prevent fore-and-aft movement of the locomotive on the rollers. 
3. Colonel Stephens Railcars
These were tiny railcars which usually ran in pairs and occasionally with a filler coach. Stephens bought a number of sets based a on Ford chassis and they were known as Railmotors.
Ford Railmotor set No. 1 arrived on the Kent and East Sussex Light Railway in 1922, featuring in the Commercial Motor Magazine of 12th December 1922.  It came from Edmonds of Thetford. The bodywork was made by Eaton Coachworks of Cringleford. The seating capacity was 20 in each car. Later models had the same capacity in seating but some design differences. Set No. 1 can be seen in the picture below. Compared with the locomotive, it is small!
Railmotor No. 1 on the K&ESR at Tenterden in 1923, sitting alongside an Ilfracombe goods loco (c) Colonel Stephens Museum. In its early years the railmotor sets had headlamps either side of the radiator. Later a headlamp was sited on the roof. 
1. W.T. Thornwell; Forward From Steam; in A. Williams; Railway World Annual; Ian Allan, Sheperton, Surrey, 1973, p76-84.
2. https://www.warwickshirerailways.com/gwr/gwrwm421.htm, accessed on 2nd January 2020.
3. http://mikes.railhistory.railfan.net/r146.html, accessed on 2nd January 2020.
5. https://www.beervisits.eu/brewery-visit/brewery-visit-europe/246-bv-ireland-republic/961-dublin-co-dublin-guinness-brewery-part-2, accessed on 26th April 2019.
6. https://www.irsociety.co.uk/Archives/22/Guinness.htm, accessed on 26th April 2019.
7. http://douglas-self.com/MUSEUM/LOCOLOCO/gaugechange/gaugechange.htm, accessed on 27th April 2019.
8. https://www.google.com/search?q=guinness+broad+gauge+engines&client=tablet-android-lenovo&prmd=sinv&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiO8Y3O5_DhAhV0QRUIHWUvB-MQ_AUoAnoECAwQAg&biw=1280&bih=800#imgdii=S5Hd0zqysW0cnM:&imgrc=2A9QGRU_nRYBPM:, accessed on 27th April 2019.
9. http://archive.commercialmotor.com/article/16th-february-1932/49/the-michelin-railcar-in-england, accessed non 3rd January 2020.
10. http://www.disused-stations.org.uk/c/cambridge/index6.shtml, accessed on 3rd January 2020.
11. http://colonelstephenssociety.co.uk/rollingstock%20topics/ford%20railmotors.html, accessed on 27th July 2019.
12. https://twitter.com/KandESRailway/status/923509399003549698?s=19, accessed on 27th July 2019.