IMHO, there are many alternatives to Exacq, but it depends on what market you are looking at. Here the ones I am familiar with are in no particular order.
* Salient - Thick client interface, server or cloud based. Same cost, most of the same functionality, not quite as good performance, older code, software only as well as appliances and hybrid models. Why go with them? Price
* VideoInsight - See above minus the cloud, plus a good web viewer. Software only as well as Dell servers. No Hybrid, but have encoders. Why go with them? Price
* ipConfigure - Web based interface, server or cloud based. Slightly higher cost, more enterprise functionality, less lower end functionality, Software only but make own appliances. Have License Plate Recognition (LPR) and Gigapixel cameras. No Hybrid models but interface with encoders. Why go with them? Want web based VMS, Gigapixel, LPR
* Milestone - Thick client based but web client has HTML 5 interface, higher overall cost, more funcationality. Software only but have partners that build appliances in the US. One such partner has created a hybrid model. Why go with them? Good UI, 500 lb gorilla, great camera support
* Avigilon - Thick client based, but with a web client as well. higher overall cost but no re-occuring costs. Most functionality met, but not all. Software only but rebrand Dell for their appliances. No Hybrid models but make own encoders. Also make own cameras, sell network switches, and viewing work stations. Why go with them? Good quality megapixel camera, Everything from one company so you know it works, if it does not, one throat to choke.
* 3VR - Thick client based, higher overall cost. Some functionality but not all. Software only but mostly sell their own appliances. Hybrid and NVR only models. Have video analytics that are mostly OEMed. Why go with them? Retail install
I am sure I have made a few mistakes and missed a few, but this is what I threw together in 15 minutes. I did not include Genetec because they do not compete well with Exacq and I do not think they are a real alternative VMS.