Q: Can I create a proprietary software, and sell it with Smarty?
A: Yes, you can. Smarty is licensed under the [LGPL] and distributing an unmodified smarty source as part of a commercial product is just fine. Be sure it contains all the LGPL license files, copyright notices, etc. Also anywhere you mention copyrights on your own source code, you should also mention copyrights of third party software such as Smarty.

A: As far as I know the GPL licence doesn't allow any work using a GPL software in any way different by mere aggregation to be released with a licence different from GPL. For this reason LGPL licence was created. LGPL allows programs using or linking to a library to be released with a different licence.

A: The LGPL is rather liberal but you must absolutely, positively adhere to the few conditions that it implies. Please see the forum, your copy of the LGPL bundled with Smarty and the Free Software Foundation for more specific details. If you fail to do so, then the LGPL specifies that you have NO license to use the software. If in doubt, ask and if you are producing a commercial application, you are encouraged to seek qualified legal advice.

LGPL 이라고 합니다 :)

유지보수입장에선 탁월하고 우수한 기능에 적극 추천하고 싶지만
2가지 문제가 생기더군요

1) 초급 개발자가 공부해야하는 시간 할애가 필요하고, 시행착오가 있었습니다.
2) 사용자쪽에 사용하게 해주었를때, 사용자가 어려워하고, 다 뺐다라는 후기도 있었습니다.

저도 이 두 가지에 공감합니다.
스마티나 템플릿 언더바나 초급이나 그 근처 개발자들이 좀 어려워 하더라구요.