[angiosperm]

Nuclear submarines have no use for a working fluid that boils below 100 C. Indeed, they pressurize the water so that the boiling point is well above that point, because they have no difficulty heating water well above that.

Steam is used everywhere despite that it is quite corrosive, mainly because it is cheap.

[pi-e-sigma]

You clearly don't know what you are talking about. Water steam is a perfect medium for turbines because of its favorable thermodynamic properties, mainly high specific heat allowing water steam to absorb large amount of thermal energy. Also water steam is not corrosive because water itself is not corrosive. It's the dissolved minerals making it corrosive and that's why water used for turbines is purified first.

[angiosperm]

Yet, steam turbines attached to nuke and coal plants spend 10-20% of their time offline, being overhauled mainly because of high-temperature/high-pressure steam's corrosiveness.

Cold distilled water is not corrosive. Superheated steam, howsoever pure, little resembles cold liquid water in any detail. Furthermore, hot water will pick up minerals from whatever it runs through.

Many materials that are not especially corrosive as cold liquids behave quite differently at extreme pressure and temperature. Water has uncommon valuable thermodynamic properties, but not uniquely so; its chief virtue is that it is good enough and cheap.

[pi-e-sigma]

OK, give me an example of one such liquid from your list of 'many' that has all the desired properties of water and doesn't have any undesired, such as being a poison. You can't because there aren't any.