(written from a Production point of view)
Round 2 LLC is an American company, founded by entrepreneur Tom Lowe in 2005 and based in South Bend, Indiana, that specializes in model kits, toys and die-cast collectibles. 
In 2007, they purchased the Aluminum Model Toys, Polar Lights and MPC model kit lines from their prior owners, Racing Champions. Round 2 LLC relaunched each of the product lines under their own original brand names, and for the first time in a number of years, all American-licensed Star Trek model kits, marketed since 2007, were being produced by a single company.
Round 2 markets their model kits internationally themselves, and has only once extended an one-time-only sub-license for a limited number of their kits to the Japanese model and kit company Platz, which marketed four kits in 2010 under the combined brand name "AMT/Ertl-Platz" for the Japanese market only on the occasion of the 20th anniversary of Star Trek: The Next Generation's premiere in that market.
The only other company that as of 2021 holds an official license for Star Trek model kits is the German Revell company, which managed to extend the license it held for the Star Trek: Voyager model kit line as well as new products originating from Star Trek: The Original Series and the alternate reality Star Trek films, albeit for the European Union only. The status of the American license of the Voyager model kit line, originally held by the US Revell-Monogram company, was until 2021 unclear, as no Voyager model kits had been marketed in the North-American home market since 1997.  Having presumably just simply expired, the American license was up for grabs for Round 2 at the start of 2021, though it did entail the creation of brand new expensive production casting molds for the 1:1000 scale line of Polar Lights where a new USS Voyager model kit was slated to appear later that year,  as the original ones were turned over to Revell Germany when they renegotiated their license extension around 2007, the same year Round 2 acquired its current holdings.
Incidentally, Round 2 also holds the American license for the alternate reality films, and had planned through Polar Lights to start with releases in 2010, but ultimately decided to forego on the line due to the mixed reception of those films by the traditional fanbase. As a result, only the European collectors were provided with a model kit of the alternate reality Enterprise through Revell Germany. However, with the acquisition of the Voyager license, all officially licensed Star Trek model kits are for the first time since 1997 reunified under one producer's roof as far as the North-American home market is concerned. Some Star Trek-related Round 2 brands were exchanged with Tomy, the current owner of Racing Champions (RC2) in 2011.