Wikipedia:

The Fiat–Revelli Modello 1914 was an Italian water-cooled medium machine gun produced from 1914 to 1918. It was the standard machine-gun of the Italian Army in the First World War, and was used in limited numbers into the Second World War.[1]

It was very similar to the Maxim in appearance (in fact it had the same air-cooling jacket and tripod), even though its internal workings were completely different.
Some sources claim that it had a cartridge-oiling system, but the weapon manual does not mention its presence, and it seems that only a 1930 version briefly incorporated such a system.[2] It was fed from a 50-round integral magazine divided in ten compartments, each fed from a rifle clip, an arrangement that made it rather slow to reload, prone to malfunction and very uncomfortable in sustained-fire role because of this magazine arrangement.
It was chambered for the 6.5×52mm Mannlicher–Carcano, which eased logistics (as it was the same cartridge of the Carcano rifle) but made it somewhat underpowered compared to higher-calibre weapons, weighed 17 kg (37 lb) (the tripod weighed 21.5 kg (47 lb)) and had a firing rate of 400-500 rpm (rounds-per-minute), rather low for this type of machine gun.[3]
An interesting feature was the presence of select-fire, which allowed for the choice between single shot, "normal" fire and full automatic fire.

Specifications

Weight 17 kg gun (without water) + 22.4 kg tripod
Length 1180 mm
Barrel length 654 mm
Cartridge 6.5×52mm Carcano
Rate of fire 400-500 rpm
Feed system 50-round magazine
Sights Iron

From Small Arms Defense Journal, http://www.sadefensejournal.com/wp/?p=823. Article by Robert G. Segel on 10 January, 2012.

"FIAT Revelli Machine Gun
In 1908, a young Italian inventor from Rome by the name of Captain Bethel Abiel Revelli, applied for his first patent on machine guns. The first of many, Revelli’s name would ultimately become synonymous with Italian automatic weapon design and would become a high ranking military officer in the Italian army.
Revelli had already caught the attention of the Italian army when he earlier designed (circa 1906) a swinging wedge to lock the breech of a pistol that would become the basis of the Glisenti Model 1910 semiautomatic pistol. The Glisenti M1910 became the standard Italian side-arm for non-commissioned officers and enlisted men of machine gun and artillery detachments until replaced by the Beretta Model 34 in 1934. In 1908, Revelli used a similar system as he began work on his water-cooled machine gun using a delayed blowback operating system. He additionally designed a unique feed system using a metal cage containing the cartridges rather than a belt or feed strip system. The gun was chambered in the standard 6.5mm (.256 caliber) Italian service cartridge.
Select-fire
One of the interesting aspects of his design was that the gun is select-fire. There is a three-position lever located directly above the thumb trigger that served as the safety and fire control selector. To the left is marked “LENTA” (slow) that enabled the weapon to fire in single shot mode. Vertically in the center is marked “SICURA” (safe) and is the safety setting for the weapon. To the right is marked “RAPIDA” (fast) allowing the weapon to fire until the trigger is released or the ammunition is expended. (While it is logical to have the different firing modes to each side with the safety setting in the center, the lever easily can be bumped or pushed to one side rendering the gun in an unsafe condition; resulting in an accidental discharge if the trigger is pushed by accident.)
Cocking Handle
The cocking handle is designed in the shape of a cross. This allows the cocking handle to be grasped on both sides with the fingers of one hand and drawn to the rear. It is incorporated in the rear portion of the bolt and protrudes exposed from the rear of the gun along the topmost portion of the receiver. The cocking handle recoils with the bolt striking a buffer plate located directly in front of the top portion of the spade grips. With a cyclic rate of approximately 500 rounds per minute, the exposed cocking handle, traveling 5-1/4 inches back and forth, proved hazardous to any finger that strayed into its operating path.
Water-Cooling System
Revelli used a water cooling system that was atypical of water-cooled weapons of that era. Most all water-cooled machine guns of that time (Maxim, Vickers, Schwarzlose and, later, the Browning) used a steam condensing tube system within the water jacket to allow the steam pressure build-up to escape through a steam condensing port. Revelli used a water circulation system in his gun. Water was introduced into the water jacket by a filling hole located at the top of the rear of the water jacket just in front of the trunnion as is common to water-cooled guns of that period. However, instead of a steam condensing device, there are two water valve fixtures located directly beneath the water jacket, in front of the trunnion. A manually operated water can and pump with two hoses, attached to the two water valves. The forward valve returned water back into the water jacket and the rear valve drew water and steam vapor out of the water jacket. This operation was accomplished by an assistant gunner turning a pump handle on the water can.
Cartridge Oiling System
It should be noted that almost every reference book discussing the FIAT Revelli Model 1914 mentions that since the gun was a delayed blow-back weapon, which resulted in violent extraction of the fired cartridge case, an oil pump is incorporated within the receiver to lubricate the cartridges prior to chambering. This is not true. The FIAT Revelli Model 1914 does not have, nor did it ever have, a cartridge oiling system. A later version in the 1930’s briefly incorporated such a system but was quickly replaced with a barrel with a fluted chamber to ease extraction.
Tripod
The tripod is of a standard configuration with two front legs that may be folded to the rear for transportation purposes. There is no accommodation for a seat to be attached to the rear leg. The tripod head contains a dove-tail mounting bracket that corresponds to a matching mount on the bottom of the gun directly under the feed-way. The gun is placed on the mount by sliding the gun rearward into the corresponding dove-tail grooves. To the rear of the tripod head is a spring loaded stud that slips into a hole located approximately mid way underneath the bottom of the receiver. This locks the gun in position on the tripod head and prevents any movement to the front or rear.
There is a large friction handle on the right side of the tripod head that allows for large traversing movement. For more precise traversing movement, another friction lock is located at the rear of the tripod head that allows more accurate traversing movement along an arced path with adjustable traverse stops.
Elevation is controlled by two knobs located on the left side of the rear leg attached to the elevation gear. The upper knob frees or locks the toothed elevation arc for large elevation or depression adjustments. The lower knob provides for finer elevation or depression correction.
World War I
Revelli spent a number of years perfecting his machine gun design and worked with the FIAT (Fabricca Italia Automobiles Torino) automobile company, who built his prototypes, in Turin, Italy. The Italian War Ministry gave the gun frequent trials where the gun performed well. But, the government was indecisive and no further development was encouraged. World War I changed all that.
Italy, like many countries that purchased machine guns on the world market, suddenly found themselves without a reliable source of foreign manufactured arms. Sources quickly dried up for Maxim, Vickers, St. Etienne and Colt guns as they were all desperately being used by the warring factions. Italy realized that, (1) Revelli’s machine gun had performed well in their trials and, (2) FIAT had the capacity and machinery to immediately begin production with the ability to expand production as needed. Thus, Revelli’s machine gun was quickly approved and adopted as the FIAT Revelli Modello 1914 and, without delay, put into production. The FIAT Revelli M1914 remained in front line service for almost thirty years until Italy capitulated in 1943 in World War II. In a modernization program in 1935, the water-cooled jacket was removed in favor of air cooling.
Aircraft Use
The Italians were the first to use the airplane as a weapon of warfare during the Italo-Turkish war that ended in October, 1912. On January 7, 1915, the Italian Council of Ministers issued decree No. 11, which authorized an independent air service and when Italy declared war on Austria-Hungary on May 23, 1915, her air strength on mobilization consisted of twelve squadrons with four forming.
By late 1915, new aircraft were being introduced into Italian service, all of which required machine guns for defense. As to be expected, the standard army gun was adopted, the FIAT Revelli Model 1914."

The four excellent photos of the Fiat are from the James Julia auction site.