14TP

The 14TP was a Polish prototype for a medium cruiser tank that was never completed due to the start of the World War II.
It was designed in 1938 and was heavily based on the previous 10TP with the idea of improving the performance of this last one.
The armour on each side wouldn't be thicker than 35mm and it could have two type of turrets, either one with a 37mm Bofors cannon or one with a 47mm gun and it was planned to be powered by a 300hp Maybach engine to make it more powerful and fast.
The tank was 60% completed by the end of 1938 and the first tests were planned for March 1939, however it turned out that Maybach company (the builder of the engines) had sent two defective copies of the engines, so the tank couldn't be assembled. This leaded to the talks about the replacement of the defective parts with better ones and that, leaded to the halt of the project in the summer of 1939 and, shortly after, Germany invaded and the plans fell into German hands.

Sources:
1. https://en.wikipedia.org/wiki/14TP
2. Salamander Books - The Illustrated Encyclopedia of the World's Tanks and AFVs

10TP Tank

The 10TP was a Polish light cruiser tank prototype. It was designed back in 1935 by a team of engineers leaded by Major Rudolf Gundlach as "natural" development of the previous 7TP light tank.
By 1936, even if the design wasn't complete, it was approved to be included in the programme of armoured forces that was part of a bigger plan to modernize and expand the Polish Army during the period of 1936-1942. This tank was expected to be part of the tank battalions for the newly created motorised units.
The prototype was started to be built in 1937 at the State Engineering Plants, located at the outskirts of Warsaw, where every Polish tank during the period of 1931-1939 was manufactured. At the same time, two motorised cavalry brigades were raised, in order to be equipped with this tank.
It was completed on 16th August 1938 and its trials were kept in secret as the activities of the German Abwehr were becoming more intensive. In January 1939 it was further tested and it managed to travel a distance of 610km (379 milles). Before it could be massly produced, Poland was invaded by Germany in September 1939 and any further development was halted.

Sources:
1. https://en.wikipedia.org/wiki/10TP
2. Salamander Books - The Illustrated Encyclopedia of the World's Tanks and AFVs.