2.7 is

• Faster AI and Turn processing than 2.5
• Requires less memory than 2.5 (great is you only have 4-8GB of RAM)
• Access to some good looking 2.7 maps, that use isAI to aid the AIs game play
• Enhanced Purchase Panel: It is improved to remember and retains your older troop purchases when you accidentally overbuy.
• Shows on Status Bar, Territory Units: A quick-glance now lists the exact units in a given territory for better tactical awareness.
• Shows on Status Bar, the TT/SZ relationship(war, neutral, allied) of territories (Really good in FFA maps)
• Shows on Status Bar, Map Zoom: Map viewing is more flexible allows for a custom zoom capability up to 200%.
• Shows any map missing icons as a placeholder square icon. (A must for map makers)

Get it here
https://github.com/triplea-game/triplea/releases

You can also have 2.5 installed at the same time.

Written for 2.6, but it still applies to 2.7
https://forums.triplea-game.org/topic/3724/how-to-have-triplea-2-5-2-6-installed-at-the-same-time