The best free alternative to QtiPlot is SciDaVis, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to QtiPlot and six of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to QtiPlot are LabPlot (Free, Open Source), Veusz (Free), Kst (Free, Open Source) and DataMelt (Free Personal, Open Source).
LabPlot provides an easy way to create, manage and edit plots. It allows you to produce plots based on data from a spreadsheet or on data imported from external files. Plots can be exported to several pixmap and vector graphic formats.
Veusz is a GUI scientific plotting and graphing package. It is designed to produce publication-ready Postscript or PDF output. SVG, EMF and bitmap export formats are also supported. The program runs under Unix/Linux, Windows or Mac OS X, and binaries are provided.