Muang Ngeun is a town in Northern Laos.
Muang Ngeun isn't really a town, but series of mostly Tai Lue villages spread out along the road.
The main reason to come to Muang Ngeun is to cross the border from Ban Huay Kon (Thailand). Many don't know it, but the border with Thailand (Ban Huay Kon–Muang Ngeun) has been open for a year or two. You can get a visa-on-arrival on both sides of the border. You need to bring a picture for the visa.
The bus onwards to Udom Xai is at 12:00, so if you don't want to spend a night in Muang Ngeun— not a bad thing—you should cross the border in the morning.
It's also possible to get the slow boat heading north from Pak Beng (departs 08:30) to drop you at the road to Muang Ngeun. Costs 30,000 kip. At the top of the hill is a sort of bus station (empty car park with a hut by the entrance with a friendly Lao in it). From there you can get transport for 30,000 kip to Muang Ngeun.