closed fonts, how to remove double lines in Inkscape. There's a "pro" version which has extra editing capabilities.
The fonts appear similar to Machine Tool or Hershey. A free font pack is available which adds extra fonts. The free version has basic tools to set size, spacing, angle, curve etc. It will generate either a DXF file or G-code toolpath for whatever text you enter.
Go and read Evilmadscientist's page on their Hershey text extension for Inkscape. Summary of single-line fonts (10/01/15) What's a single-line font?