SpecMerge
Astro-Software
Merge two spectra in VisualSpec format *.spc to one spectrum
Features 
- Freeware
- Automatic level of flux (Y-axis)
- Additional CSV file output possible
Known problem of VSpec: : Only if calibrated specs are mergeg: in the merged area, VSpec can display the spec-graphic different in X-axis to the real pixel values (shown on the menu line in VSpec)! That means the absorbtion-glen is shown shifted to the real data position.
System requirements
Windows 7 with .Net Framework 4.5 or Windows 8 (8.1), 32 or 64 Bit (Download)
Microsoft Visual C++ Redistributeable 2010 or 2012 (Download)
Download and read at first readme.txt
Download freeware SpecMerge: Setup.exe Version 1.1 (2014-11-29)