All Non-manifold

Blender Development Fund
Asset Library
Blender Development Fund
Asset Library
Model Inspector
$9.99

Lonely Tree Studios in Addons

QuadLab Mesh Cleaner
$24.90

QuadLab Tools in Addons

Find Me
$32

3DF in Addons

Check Mesh
$7.77

KewlSheet in Addons

Mesh Check GPU Edition
$3.50

Pistiwique in Addons

Extra Mesh Editor
$6.50 Dev Fund Contributor

EBTRR in Addons

PUNCHit
$9.99-$149.99

MACHIN3 in Addons