Thermodynamics is a relatively recent physical science that was born with calorimetry and thermometry experiments: so heat remains the central concept in relation with other forms of energy. The coupling between various forms is essential and related to conversion processes. The first conversion process that was analyzed was the thermo mechanical one, at the time of Carnot. Equilibrium Thermodynamics was fruitful in connection with the efficiency concept, to qualify engines. But since that time, mass and heat transfers studies have been strongly developed (thermo kinetics), as well as second law aspects of thermodynamics. It results new appraisal for energy Systems and processes, relevant of a true thermodynamics approach. This was initiated by Onsager at the beginning of the 20th century, by analyzing the relation between fluxes and forces (gradients) from a general, but linear point of view. More recently, it was developed through a lumped analysis for Systems by Chambadal and Novikov in 1957. It was rediscovered in 1975, by Curzon and Ahlborn. And since this work, a lot of books and publications have been proposed in the literature. A review of them is proposed here, on the basis of a synthesis due to the lack of place. The author's works are analysed and compared to the literature too. It results some original remarks and proposal relative to the obtained results: Comparison of entropy ratio method to entropy flux method, Comparison of endoreversible case to irreversible case, Comparison of adiabatic and non adiabatic Systems, Comparison of constrained and non constrained Systems. Main consequences of these comparisons are given, and future perspectives evoked on the main Systems categories (engines, reverse machines, other eventual configurations). Conclusion is that FDOT (Finite Dimensions Thermodynamics) appears as a promising tool to be enlarged in the future.