Fox DOSS dropper post, 31.6mm, 100mm drop with remote.
3 position dropper with 40mm and 100mm drop positions. Small mark on stanchion pictured.
Has been very reliable, not as smooth or as long as some newer droppers but simple and effective. The thumb trigger lever can be flipped to go on the left or right, and has adjustable reach.
£100 posted in UK, or collect from Maidstone, Kent.