Complex sentence: The Brügger & Thomet MP9 is basically a Steyr TMP with a stock that folds to the right side of the weapon and has an integrated Picatinny rail.
Split into simpler sentences: The Brügger & Thomet MP9 is a development of the Steyr TMP. Differences from the TMP include a stock that folds to the right side of the weapon, and an integrated Picatinny rail.